Let's get this math done. We have 780 and we're going to multiply it by 89. This is the same as taking 780 and adding it to itself 89 times.
Step 1: 0 + 780 = 780
Step 2: 780 + 780 = 1560
Step 3: 1560 + 780 = 2340
Step 4: 2340 + 780 = 3120
Step 5: 3120 + 780 = 3900
Step 6: 3900 + 780 = 4680
Step 7: 4680 + 780 = 5460
Step 8: 5460 + 780 = 6240
Step 9: 6240 + 780 = 7020
Step 10: 7020 + 780 = 7800
Step 11: 7800 + 780 = 8580
Step 12: 8580 + 780 = 9360
Step 13: 9360 + 780 = 10140
Step 14: 10140 + 780 = 10920
Step 15: 10920 + 780 = 11700
Step 16: 11700 + 780 = 12480
Step 17: 12480 + 780 = 13260
Step 18: 13260 + 780 = 14040
Step 19: 14040 + 780 = 14820
Step 20: 14820 + 780 = 15600
Step 21: 15600 + 780 = 16380
Step 22: 16380 + 780 = 17160
Step 23: 17160 + 780 = 17940
Step 24: 17940 + 780 = 18720
Step 25: 18720 + 780 = 19500
Step 26: 19500 + 780 = 20280
Step 27: 20280 + 780 = 21060
Step 28: 21060 + 780 = 21840
Step 29: 21840 + 780 = 22620
Step 30: 22620 + 780 = 23400
Step 31: 23400 + 780 = 24180
Step 32: 24180 + 780 = 24960
Step 33: 24960 + 780 = 25740
Step 34: 25740 + 780 = 26520
Step 35: 26520 + 780 = 27300
Step 36: 27300 + 780 = 28080
Step 37: 28080 + 780 = 28860
Step 38: 28860 + 780 = 29640
Step 39: 29640 + 780 = 30420
Step 40: 30420 + 780 = 31200
Step 41: 31200 + 780 = 31980
Step 42: 31980 + 780 = 32760
Step 43: 32760 + 780 = 33540
Step 44: 33540 + 780 = 34320
Step 45: 34320 + 780 = 35100
Step 46: 35100 + 780 = 35880
Step 47: 35880 + 780 = 36660
Step 48: 36660 + 780 = 37440
Step 49: 37440 + 780 = 38220
Step 50: 38220 + 780 = 39000
Step 51: 39000 + 780 = 39780
Step 52: 39780 + 780 = 40560
Step 53: 40560 + 780 = 41340
Step 54: 41340 + 780 = 42120
Step 55: 42120 + 780 = 42900
Step 56: 42900 + 780 = 43680
Step 57: 43680 + 780 = 44460
Step 58: 44460 + 780 = 45240
Step 59: 45240 + 780 = 46020
Step 60: 46020 + 780 = 46800
Step 61: 46800 + 780 = 47580
Step 62: 47580 + 780 = 48360
Step 63: 48360 + 780 = 49140
Step 64: 49140 + 780 = 49920
Step 65: 49920 + 780 = 50700
Step 66: 50700 + 780 = 51480
Step 67: 51480 + 780 = 52260
Step 68: 52260 + 780 = 53040
Step 69: 53040 + 780 = 53820
Step 70: 53820 + 780 = 54600
Step 71: 54600 + 780 = 55380
Step 72: 55380 + 780 = 56160
Step 73: 56160 + 780 = 56940
Step 74: 56940 + 780 = 57720
Step 75: 57720 + 780 = 58500
Step 76: 58500 + 780 = 59280
Step 77: 59280 + 780 = 60060
Step 78: 60060 + 780 = 60840
Step 79: 60840 + 780 = 61620
Step 80: 61620 + 780 = 62400
Step 81: 62400 + 780 = 63180
Step 82: 63180 + 780 = 63960
Step 83: 63960 + 780 = 64740
Step 84: 64740 + 780 = 65520
Step 85: 65520 + 780 = 66300
Step 86: 66300 + 780 = 67080
Step 87: 67080 + 780 = 67860
Step 88: 67860 + 780 = 68640
Step 89: 68640 + 780 = 69420

So, 780*89 = 69420