Let's get this math done. We have 729 and we're going to multiply it by 39. This is the same as taking 729 and adding it to itself 39 times.
Step 1: 0 + 729 = 729
Step 2: 729 + 729 = 1458
Step 3: 1458 + 729 = 2187
Step 4: 2187 + 729 = 2916
Step 5: 2916 + 729 = 3645
Step 6: 3645 + 729 = 4374
Step 7: 4374 + 729 = 5103
Step 8: 5103 + 729 = 5832
Step 9: 5832 + 729 = 6561
Step 10: 6561 + 729 = 7290
Step 11: 7290 + 729 = 8019
Step 12: 8019 + 729 = 8748
Step 13: 8748 + 729 = 9477
Step 14: 9477 + 729 = 10206
Step 15: 10206 + 729 = 10935
Step 16: 10935 + 729 = 11664
Step 17: 11664 + 729 = 12393
Step 18: 12393 + 729 = 13122
Step 19: 13122 + 729 = 13851
Step 20: 13851 + 729 = 14580
Step 21: 14580 + 729 = 15309
Step 22: 15309 + 729 = 16038
Step 23: 16038 + 729 = 16767
Step 24: 16767 + 729 = 17496
Step 25: 17496 + 729 = 18225
Step 26: 18225 + 729 = 18954
Step 27: 18954 + 729 = 19683
Step 28: 19683 + 729 = 20412
Step 29: 20412 + 729 = 21141
Step 30: 21141 + 729 = 21870
Step 31: 21870 + 729 = 22599
Step 32: 22599 + 729 = 23328
Step 33: 23328 + 729 = 24057
Step 34: 24057 + 729 = 24786
Step 35: 24786 + 729 = 25515
Step 36: 25515 + 729 = 26244
Step 37: 26244 + 729 = 26973
Step 38: 26973 + 729 = 27702
Step 39: 27702 + 729 = 28431

So, 729*39 = 28431