OK, let's crack this. We're given 339 and our task is to multiply it by 39. Essentially, we'll be adding 339 to itself 39 times.
Step 1: 0 + 339 = 339
Step 2: 339 + 339 = 678
Step 3: 678 + 339 = 1017
Step 4: 1017 + 339 = 1356
Step 5: 1356 + 339 = 1695
Step 6: 1695 + 339 = 2034
Step 7: 2034 + 339 = 2373
Step 8: 2373 + 339 = 2712
Step 9: 2712 + 339 = 3051
Step 10: 3051 + 339 = 3390
Step 11: 3390 + 339 = 3729
Step 12: 3729 + 339 = 4068
Step 13: 4068 + 339 = 4407
Step 14: 4407 + 339 = 4746
Step 15: 4746 + 339 = 5085
Step 16: 5085 + 339 = 5424
Step 17: 5424 + 339 = 5763
Step 18: 5763 + 339 = 6102
Step 19: 6102 + 339 = 6441
Step 20: 6441 + 339 = 6780
Step 21: 6780 + 339 = 7119
Step 22: 7119 + 339 = 7458
Step 23: 7458 + 339 = 7797
Step 24: 7797 + 339 = 8136
Step 25: 8136 + 339 = 8475
Step 26: 8475 + 339 = 8814
Step 27: 8814 + 339 = 9153
Step 28: 9153 + 339 = 9492
Step 29: 9492 + 339 = 9831
Step 30: 9831 + 339 = 10170
Step 31: 10170 + 339 = 10509
Step 32: 10509 + 339 = 10848
Step 33: 10848 + 339 = 11187
Step 34: 11187 + 339 = 11526
Step 35: 11526 + 339 = 11865
Step 36: 11865 + 339 = 12204
Step 37: 12204 + 339 = 12543
Step 38: 12543 + 339 = 12882
Step 39: 12882 + 339 = 13221

So, 339*39 = 13221