OK, let's work through this together. We're starting with 129 and we're going to multiply it by 80, which means we add 129 to itself 80 times.
Step 1: 0 + 129 = 129
Step 2: 129 + 129 = 258
Step 3: 258 + 129 = 387
Step 4: 387 + 129 = 516
Step 5: 516 + 129 = 645
Step 6: 645 + 129 = 774
Step 7: 774 + 129 = 903
Step 8: 903 + 129 = 1032
Step 9: 1032 + 129 = 1161
Step 10: 1161 + 129 = 1290
Step 11: 1290 + 129 = 1419
Step 12: 1419 + 129 = 1548
Step 13: 1548 + 129 = 1677
Step 14: 1677 + 129 = 1806
Step 15: 1806 + 129 = 1935
Step 16: 1935 + 129 = 2064
Step 17: 2064 + 129 = 2193
Step 18: 2193 + 129 = 2322
Step 19: 2322 + 129 = 2451
Step 20: 2451 + 129 = 2580
Step 21: 2580 + 129 = 2709
Step 22: 2709 + 129 = 2838
Step 23: 2838 + 129 = 2967
Step 24: 2967 + 129 = 3096
Step 25: 3096 + 129 = 3225
Step 26: 3225 + 129 = 3354
Step 27: 3354 + 129 = 3483
Step 28: 3483 + 129 = 3612
Step 29: 3612 + 129 = 3741
Step 30: 3741 + 129 = 3870
Step 31: 3870 + 129 = 3999
Step 32: 3999 + 129 = 4128
Step 33: 4128 + 129 = 4257
Step 34: 4257 + 129 = 4386
Step 35: 4386 + 129 = 4515
Step 36: 4515 + 129 = 4644
Step 37: 4644 + 129 = 4773
Step 38: 4773 + 129 = 4902
Step 39: 4902 + 129 = 5031
Step 40: 5031 + 129 = 5160
Step 41: 5160 + 129 = 5289
Step 42: 5289 + 129 = 5418
Step 43: 5418 + 129 = 5547
Step 44: 5547 + 129 = 5676
Step 45: 5676 + 129 = 5805
Step 46: 5805 + 129 = 5934
Step 47: 5934 + 129 = 6063
Step 48: 6063 + 129 = 6192
Step 49: 6192 + 129 = 6321
Step 50: 6321 + 129 = 6450
Step 51: 6450 + 129 = 6579
Step 52: 6579 + 129 = 6708
Step 53: 6708 + 129 = 6837
Step 54: 6837 + 129 = 6966
Step 55: 6966 + 129 = 7095
Step 56: 7095 + 129 = 7224
Step 57: 7224 + 129 = 7353
Step 58: 7353 + 129 = 7482
Step 59: 7482 + 129 = 7611
Step 60: 7611 + 129 = 7740
Step 61: 7740 + 129 = 7869
Step 62: 7869 + 129 = 7998
Step 63: 7998 + 129 = 8127
Step 64: 8127 + 129 = 8256
Step 65: 8256 + 129 = 8385
Step 66: 8385 + 129 = 8514
Step 67: 8514 + 129 = 8643
Step 68: 8643 + 129 = 8772
Step 69: 8772 + 129 = 8901
Step 70: 8901 + 129 = 9030
Step 71: 9030 + 129 = 9159
Step 72: 9159 + 129 = 9288
Step 73: 9288 + 129 = 9417
Step 74: 9417 + 129 = 9546
Step 75: 9546 + 129 = 9675
Step 76: 9675 + 129 = 9804
Step 77: 9804 + 129 = 9933
Step 78: 9933 + 129 = 10062
Step 79: 10062 + 129 = 10191
Step 80: 10191 + 129 = 10320

So, 129*80 = 10320