Alright, let's solve this math problem step by step. First, we have the number 905. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 81. So, we're going to take the number 905 and add it to itself 81 times.
Step 1: 0 + 905 = 905
Step 2: 905 + 905 = 1810
Step 3: 1810 + 905 = 2715
Step 4: 2715 + 905 = 3620
Step 5: 3620 + 905 = 4525
Step 6: 4525 + 905 = 5430
Step 7: 5430 + 905 = 6335
Step 8: 6335 + 905 = 7240
Step 9: 7240 + 905 = 8145
Step 10: 8145 + 905 = 9050
Step 11: 9050 + 905 = 9955
Step 12: 9955 + 905 = 10860
Step 13: 10860 + 905 = 11765
Step 14: 11765 + 905 = 12670
Step 15: 12670 + 905 = 13575
Step 16: 13575 + 905 = 14480
Step 17: 14480 + 905 = 15385
Step 18: 15385 + 905 = 16290
Step 19: 16290 + 905 = 17195
Step 20: 17195 + 905 = 18100
Step 21: 18100 + 905 = 19005
Step 22: 19005 + 905 = 19910
Step 23: 19910 + 905 = 20815
Step 24: 20815 + 905 = 21720
Step 25: 21720 + 905 = 22625
Step 26: 22625 + 905 = 23530
Step 27: 23530 + 905 = 24435
Step 28: 24435 + 905 = 25340
Step 29: 25340 + 905 = 26245
Step 30: 26245 + 905 = 27150
Step 31: 27150 + 905 = 28055
Step 32: 28055 + 905 = 28960
Step 33: 28960 + 905 = 29865
Step 34: 29865 + 905 = 30770
Step 35: 30770 + 905 = 31675
Step 36: 31675 + 905 = 32580
Step 37: 32580 + 905 = 33485
Step 38: 33485 + 905 = 34390
Step 39: 34390 + 905 = 35295
Step 40: 35295 + 905 = 36200
Step 41: 36200 + 905 = 37105
Step 42: 37105 + 905 = 38010
Step 43: 38010 + 905 = 38915
Step 44: 38915 + 905 = 39820
Step 45: 39820 + 905 = 40725
Step 46: 40725 + 905 = 41630
Step 47: 41630 + 905 = 42535
Step 48: 42535 + 905 = 43440
Step 49: 43440 + 905 = 44345
Step 50: 44345 + 905 = 45250
Step 51: 45250 + 905 = 46155
Step 52: 46155 + 905 = 47060
Step 53: 47060 + 905 = 47965
Step 54: 47965 + 905 = 48870
Step 55: 48870 + 905 = 49775
Step 56: 49775 + 905 = 50680
Step 57: 50680 + 905 = 51585
Step 58: 51585 + 905 = 52490
Step 59: 52490 + 905 = 53395
Step 60: 53395 + 905 = 54300
Step 61: 54300 + 905 = 55205
Step 62: 55205 + 905 = 56110
Step 63: 56110 + 905 = 57015
Step 64: 57015 + 905 = 57920
Step 65: 57920 + 905 = 58825
Step 66: 58825 + 905 = 59730
Step 67: 59730 + 905 = 60635
Step 68: 60635 + 905 = 61540
Step 69: 61540 + 905 = 62445
Step 70: 62445 + 905 = 63350
Step 71: 63350 + 905 = 64255
Step 72: 64255 + 905 = 65160
Step 73: 65160 + 905 = 66065
Step 74: 66065 + 905 = 66970
Step 75: 66970 + 905 = 67875
Step 76: 67875 + 905 = 68780
Step 77: 68780 + 905 = 69685
Step 78: 69685 + 905 = 70590
Step 79: 70590 + 905 = 71495
Step 80: 71495 + 905 = 72400
Step 81: 72400 + 905 = 73305

So, 905*81 = 73305