OK, let's work through this together. We're starting with 290 and we're going to multiply it by 123, which means we add 290 to itself 123 times.
Step 1: 0 + 290 = 290
Step 2: 290 + 290 = 580
Step 3: 580 + 290 = 870
Step 4: 870 + 290 = 1160
Step 5: 1160 + 290 = 1450
Step 6: 1450 + 290 = 1740
Step 7: 1740 + 290 = 2030
Step 8: 2030 + 290 = 2320
Step 9: 2320 + 290 = 2610
Step 10: 2610 + 290 = 2900
Step 11: 2900 + 290 = 3190
Step 12: 3190 + 290 = 3480
Step 13: 3480 + 290 = 3770
Step 14: 3770 + 290 = 4060
Step 15: 4060 + 290 = 4350
Step 16: 4350 + 290 = 4640
Step 17: 4640 + 290 = 4930
Step 18: 4930 + 290 = 5220
Step 19: 5220 + 290 = 5510
Step 20: 5510 + 290 = 5800
Step 21: 5800 + 290 = 6090
Step 22: 6090 + 290 = 6380
Step 23: 6380 + 290 = 6670
Step 24: 6670 + 290 = 6960
Step 25: 6960 + 290 = 7250
Step 26: 7250 + 290 = 7540
Step 27: 7540 + 290 = 7830
Step 28: 7830 + 290 = 8120
Step 29: 8120 + 290 = 8410
Step 30: 8410 + 290 = 8700
Step 31: 8700 + 290 = 8990
Step 32: 8990 + 290 = 9280
Step 33: 9280 + 290 = 9570
Step 34: 9570 + 290 = 9860
Step 35: 9860 + 290 = 10150
Step 36: 10150 + 290 = 10440
Step 37: 10440 + 290 = 10730
Step 38: 10730 + 290 = 11020
Step 39: 11020 + 290 = 11310
Step 40: 11310 + 290 = 11600
Step 41: 11600 + 290 = 11890
Step 42: 11890 + 290 = 12180
Step 43: 12180 + 290 = 12470
Step 44: 12470 + 290 = 12760
Step 45: 12760 + 290 = 13050
Step 46: 13050 + 290 = 13340
Step 47: 13340 + 290 = 13630
Step 48: 13630 + 290 = 13920
Step 49: 13920 + 290 = 14210
Step 50: 14210 + 290 = 14500
Step 51: 14500 + 290 = 14790
Step 52: 14790 + 290 = 15080
Step 53: 15080 + 290 = 15370
Step 54: 15370 + 290 = 15660
Step 55: 15660 + 290 = 15950
Step 56: 15950 + 290 = 16240
Step 57: 16240 + 290 = 16530
Step 58: 16530 + 290 = 16820
Step 59: 16820 + 290 = 17110
Step 60: 17110 + 290 = 17400
Step 61: 17400 + 290 = 17690
Step 62: 17690 + 290 = 17980
Step 63: 17980 + 290 = 18270
Step 64: 18270 + 290 = 18560
Step 65: 18560 + 290 = 18850
Step 66: 18850 + 290 = 19140
Step 67: 19140 + 290 = 19430
Step 68: 19430 + 290 = 19720
Step 69: 19720 + 290 = 20010
Step 70: 20010 + 290 = 20300
Step 71: 20300 + 290 = 20590
Step 72: 20590 + 290 = 20880
Step 73: 20880 + 290 = 21170
Step 74: 21170 + 290 = 21460
Step 75: 21460 + 290 = 21750
Step 76: 21750 + 290 = 22040
Step 77: 22040 + 290 = 22330
Step 78: 22330 + 290 = 22620
Step 79: 22620 + 290 = 22910
Step 80: 22910 + 290 = 23200
Step 81: 23200 + 290 = 23490
Step 82: 23490 + 290 = 23780
Step 83: 23780 + 290 = 24070
Step 84: 24070 + 290 = 24360
Step 85: 24360 + 290 = 24650
Step 86: 24650 + 290 = 24940
Step 87: 24940 + 290 = 25230
Step 88: 25230 + 290 = 25520
Step 89: 25520 + 290 = 25810
Step 90: 25810 + 290 = 26100
Step 91: 26100 + 290 = 26390
Step 92: 26390 + 290 = 26680
Step 93: 26680 + 290 = 26970
Step 94: 26970 + 290 = 27260
Step 95: 27260 + 290 = 27550
Step 96: 27550 + 290 = 27840
Step 97: 27840 + 290 = 28130
Step 98: 28130 + 290 = 28420
Step 99: 28420 + 290 = 28710
Step 100: 28710 + 290 = 29000
Step 101: 29000 + 290 = 29290
Step 102: 29290 + 290 = 29580
Step 103: 29580 + 290 = 29870
Step 104: 29870 + 290 = 30160
Step 105: 30160 + 290 = 30450
Step 106: 30450 + 290 = 30740
Step 107: 30740 + 290 = 31030
Step 108: 31030 + 290 = 31320
Step 109: 31320 + 290 = 31610
Step 110: 31610 + 290 = 31900
Step 111: 31900 + 290 = 32190
Step 112: 32190 + 290 = 32480
Step 113: 32480 + 290 = 32770
Step 114: 32770 + 290 = 33060
Step 115: 33060 + 290 = 33350
Step 116: 33350 + 290 = 33640
Step 117: 33640 + 290 = 33930
Step 118: 33930 + 290 = 34220
Step 119: 34220 + 290 = 34510
Step 120: 34510 + 290 = 34800
Step 121: 34800 + 290 = 35090
Step 122: 35090 + 290 = 35380
Step 123: 35380 + 290 = 35670

So, 290*123 = 35670