Let's roll up our sleeves and solve this. We have 243 and we're going to multiply it by 73, essentially adding 243 to itself 73 times.
Step 1: 0 + 243 = 243
Step 2: 243 + 243 = 486
Step 3: 486 + 243 = 729
Step 4: 729 + 243 = 972
Step 5: 972 + 243 = 1215
Step 6: 1215 + 243 = 1458
Step 7: 1458 + 243 = 1701
Step 8: 1701 + 243 = 1944
Step 9: 1944 + 243 = 2187
Step 10: 2187 + 243 = 2430
Step 11: 2430 + 243 = 2673
Step 12: 2673 + 243 = 2916
Step 13: 2916 + 243 = 3159
Step 14: 3159 + 243 = 3402
Step 15: 3402 + 243 = 3645
Step 16: 3645 + 243 = 3888
Step 17: 3888 + 243 = 4131
Step 18: 4131 + 243 = 4374
Step 19: 4374 + 243 = 4617
Step 20: 4617 + 243 = 4860
Step 21: 4860 + 243 = 5103
Step 22: 5103 + 243 = 5346
Step 23: 5346 + 243 = 5589
Step 24: 5589 + 243 = 5832
Step 25: 5832 + 243 = 6075
Step 26: 6075 + 243 = 6318
Step 27: 6318 + 243 = 6561
Step 28: 6561 + 243 = 6804
Step 29: 6804 + 243 = 7047
Step 30: 7047 + 243 = 7290
Step 31: 7290 + 243 = 7533
Step 32: 7533 + 243 = 7776
Step 33: 7776 + 243 = 8019
Step 34: 8019 + 243 = 8262
Step 35: 8262 + 243 = 8505
Step 36: 8505 + 243 = 8748
Step 37: 8748 + 243 = 8991
Step 38: 8991 + 243 = 9234
Step 39: 9234 + 243 = 9477
Step 40: 9477 + 243 = 9720
Step 41: 9720 + 243 = 9963
Step 42: 9963 + 243 = 10206
Step 43: 10206 + 243 = 10449
Step 44: 10449 + 243 = 10692
Step 45: 10692 + 243 = 10935
Step 46: 10935 + 243 = 11178
Step 47: 11178 + 243 = 11421
Step 48: 11421 + 243 = 11664
Step 49: 11664 + 243 = 11907
Step 50: 11907 + 243 = 12150
Step 51: 12150 + 243 = 12393
Step 52: 12393 + 243 = 12636
Step 53: 12636 + 243 = 12879
Step 54: 12879 + 243 = 13122
Step 55: 13122 + 243 = 13365
Step 56: 13365 + 243 = 13608
Step 57: 13608 + 243 = 13851
Step 58: 13851 + 243 = 14094
Step 59: 14094 + 243 = 14337
Step 60: 14337 + 243 = 14580
Step 61: 14580 + 243 = 14823
Step 62: 14823 + 243 = 15066
Step 63: 15066 + 243 = 15309
Step 64: 15309 + 243 = 15552
Step 65: 15552 + 243 = 15795
Step 66: 15795 + 243 = 16038
Step 67: 16038 + 243 = 16281
Step 68: 16281 + 243 = 16524
Step 69: 16524 + 243 = 16767
Step 70: 16767 + 243 = 17010
Step 71: 17010 + 243 = 17253
Step 72: 17253 + 243 = 17496
Step 73: 17496 + 243 = 17739

So, 243*73 = 17739