OK, let's work through this together. We're starting with 790 and we're going to multiply it by 66, which means we add 790 to itself 66 times.
Step 1: 0 + 790 = 790
Step 2: 790 + 790 = 1580
Step 3: 1580 + 790 = 2370
Step 4: 2370 + 790 = 3160
Step 5: 3160 + 790 = 3950
Step 6: 3950 + 790 = 4740
Step 7: 4740 + 790 = 5530
Step 8: 5530 + 790 = 6320
Step 9: 6320 + 790 = 7110
Step 10: 7110 + 790 = 7900
Step 11: 7900 + 790 = 8690
Step 12: 8690 + 790 = 9480
Step 13: 9480 + 790 = 10270
Step 14: 10270 + 790 = 11060
Step 15: 11060 + 790 = 11850
Step 16: 11850 + 790 = 12640
Step 17: 12640 + 790 = 13430
Step 18: 13430 + 790 = 14220
Step 19: 14220 + 790 = 15010
Step 20: 15010 + 790 = 15800
Step 21: 15800 + 790 = 16590
Step 22: 16590 + 790 = 17380
Step 23: 17380 + 790 = 18170
Step 24: 18170 + 790 = 18960
Step 25: 18960 + 790 = 19750
Step 26: 19750 + 790 = 20540
Step 27: 20540 + 790 = 21330
Step 28: 21330 + 790 = 22120
Step 29: 22120 + 790 = 22910
Step 30: 22910 + 790 = 23700
Step 31: 23700 + 790 = 24490
Step 32: 24490 + 790 = 25280
Step 33: 25280 + 790 = 26070
Step 34: 26070 + 790 = 26860
Step 35: 26860 + 790 = 27650
Step 36: 27650 + 790 = 28440
Step 37: 28440 + 790 = 29230
Step 38: 29230 + 790 = 30020
Step 39: 30020 + 790 = 30810
Step 40: 30810 + 790 = 31600
Step 41: 31600 + 790 = 32390
Step 42: 32390 + 790 = 33180
Step 43: 33180 + 790 = 33970
Step 44: 33970 + 790 = 34760
Step 45: 34760 + 790 = 35550
Step 46: 35550 + 790 = 36340
Step 47: 36340 + 790 = 37130
Step 48: 37130 + 790 = 37920
Step 49: 37920 + 790 = 38710
Step 50: 38710 + 790 = 39500
Step 51: 39500 + 790 = 40290
Step 52: 40290 + 790 = 41080
Step 53: 41080 + 790 = 41870
Step 54: 41870 + 790 = 42660
Step 55: 42660 + 790 = 43450
Step 56: 43450 + 790 = 44240
Step 57: 44240 + 790 = 45030
Step 58: 45030 + 790 = 45820
Step 59: 45820 + 790 = 46610
Step 60: 46610 + 790 = 47400
Step 61: 47400 + 790 = 48190
Step 62: 48190 + 790 = 48980
Step 63: 48980 + 790 = 49770
Step 64: 49770 + 790 = 50560
Step 65: 50560 + 790 = 51350
Step 66: 51350 + 790 = 52140

So, 790*66 = 52140