Let's get this math done. We have 855 and we're going to multiply it by 39. This is the same as taking 855 and adding it to itself 39 times.
Step 1: 0 + 855 = 855
Step 2: 855 + 855 = 1710
Step 3: 1710 + 855 = 2565
Step 4: 2565 + 855 = 3420
Step 5: 3420 + 855 = 4275
Step 6: 4275 + 855 = 5130
Step 7: 5130 + 855 = 5985
Step 8: 5985 + 855 = 6840
Step 9: 6840 + 855 = 7695
Step 10: 7695 + 855 = 8550
Step 11: 8550 + 855 = 9405
Step 12: 9405 + 855 = 10260
Step 13: 10260 + 855 = 11115
Step 14: 11115 + 855 = 11970
Step 15: 11970 + 855 = 12825
Step 16: 12825 + 855 = 13680
Step 17: 13680 + 855 = 14535
Step 18: 14535 + 855 = 15390
Step 19: 15390 + 855 = 16245
Step 20: 16245 + 855 = 17100
Step 21: 17100 + 855 = 17955
Step 22: 17955 + 855 = 18810
Step 23: 18810 + 855 = 19665
Step 24: 19665 + 855 = 20520
Step 25: 20520 + 855 = 21375
Step 26: 21375 + 855 = 22230
Step 27: 22230 + 855 = 23085
Step 28: 23085 + 855 = 23940
Step 29: 23940 + 855 = 24795
Step 30: 24795 + 855 = 25650
Step 31: 25650 + 855 = 26505
Step 32: 26505 + 855 = 27360
Step 33: 27360 + 855 = 28215
Step 34: 28215 + 855 = 29070
Step 35: 29070 + 855 = 29925
Step 36: 29925 + 855 = 30780
Step 37: 30780 + 855 = 31635
Step 38: 31635 + 855 = 32490
Step 39: 32490 + 855 = 33345

So, 855*39 = 33345