OK, let's crack this. We're given 859 and our task is to multiply it by 15. Essentially, we'll be adding 859 to itself 15 times.
Step 1: 0 + 859 = 859
Step 2: 859 + 859 = 1718
Step 3: 1718 + 859 = 2577
Step 4: 2577 + 859 = 3436
Step 5: 3436 + 859 = 4295
Step 6: 4295 + 859 = 5154
Step 7: 5154 + 859 = 6013
Step 8: 6013 + 859 = 6872
Step 9: 6872 + 859 = 7731
Step 10: 7731 + 859 = 8590
Step 11: 8590 + 859 = 9449
Step 12: 9449 + 859 = 10308
Step 13: 10308 + 859 = 11167
Step 14: 11167 + 859 = 12026
Step 15: 12026 + 859 = 12885

So, 859*15 = 12885