OK, let's work through this together. We're starting with 345 and we're going to multiply it by 81, which means we add 345 to itself 81 times.
Step 1: 0 + 345 = 345
Step 2: 345 + 345 = 690
Step 3: 690 + 345 = 1035
Step 4: 1035 + 345 = 1380
Step 5: 1380 + 345 = 1725
Step 6: 1725 + 345 = 2070
Step 7: 2070 + 345 = 2415
Step 8: 2415 + 345 = 2760
Step 9: 2760 + 345 = 3105
Step 10: 3105 + 345 = 3450
Step 11: 3450 + 345 = 3795
Step 12: 3795 + 345 = 4140
Step 13: 4140 + 345 = 4485
Step 14: 4485 + 345 = 4830
Step 15: 4830 + 345 = 5175
Step 16: 5175 + 345 = 5520
Step 17: 5520 + 345 = 5865
Step 18: 5865 + 345 = 6210
Step 19: 6210 + 345 = 6555
Step 20: 6555 + 345 = 6900
Step 21: 6900 + 345 = 7245
Step 22: 7245 + 345 = 7590
Step 23: 7590 + 345 = 7935
Step 24: 7935 + 345 = 8280
Step 25: 8280 + 345 = 8625
Step 26: 8625 + 345 = 8970
Step 27: 8970 + 345 = 9315
Step 28: 9315 + 345 = 9660
Step 29: 9660 + 345 = 10005
Step 30: 10005 + 345 = 10350
Step 31: 10350 + 345 = 10695
Step 32: 10695 + 345 = 11040
Step 33: 11040 + 345 = 11385
Step 34: 11385 + 345 = 11730
Step 35: 11730 + 345 = 12075
Step 36: 12075 + 345 = 12420
Step 37: 12420 + 345 = 12765
Step 38: 12765 + 345 = 13110
Step 39: 13110 + 345 = 13455
Step 40: 13455 + 345 = 13800
Step 41: 13800 + 345 = 14145
Step 42: 14145 + 345 = 14490
Step 43: 14490 + 345 = 14835
Step 44: 14835 + 345 = 15180
Step 45: 15180 + 345 = 15525
Step 46: 15525 + 345 = 15870
Step 47: 15870 + 345 = 16215
Step 48: 16215 + 345 = 16560
Step 49: 16560 + 345 = 16905
Step 50: 16905 + 345 = 17250
Step 51: 17250 + 345 = 17595
Step 52: 17595 + 345 = 17940
Step 53: 17940 + 345 = 18285
Step 54: 18285 + 345 = 18630
Step 55: 18630 + 345 = 18975
Step 56: 18975 + 345 = 19320
Step 57: 19320 + 345 = 19665
Step 58: 19665 + 345 = 20010
Step 59: 20010 + 345 = 20355
Step 60: 20355 + 345 = 20700
Step 61: 20700 + 345 = 21045
Step 62: 21045 + 345 = 21390
Step 63: 21390 + 345 = 21735
Step 64: 21735 + 345 = 22080
Step 65: 22080 + 345 = 22425
Step 66: 22425 + 345 = 22770
Step 67: 22770 + 345 = 23115
Step 68: 23115 + 345 = 23460
Step 69: 23460 + 345 = 23805
Step 70: 23805 + 345 = 24150
Step 71: 24150 + 345 = 24495
Step 72: 24495 + 345 = 24840
Step 73: 24840 + 345 = 25185
Step 74: 25185 + 345 = 25530
Step 75: 25530 + 345 = 25875
Step 76: 25875 + 345 = 26220
Step 77: 26220 + 345 = 26565
Step 78: 26565 + 345 = 26910
Step 79: 26910 + 345 = 27255
Step 80: 27255 + 345 = 27600
Step 81: 27600 + 345 = 27945

So, 345*81 = 27945