OK, let's crack this. We're given 87 and our task is to multiply it by 15. Essentially, we'll be adding 87 to itself 15 times.
Step 1: 0 + 87 = 87
Step 2: 87 + 87 = 174
Step 3: 174 + 87 = 261
Step 4: 261 + 87 = 348
Step 5: 348 + 87 = 435
Step 6: 435 + 87 = 522
Step 7: 522 + 87 = 609
Step 8: 609 + 87 = 696
Step 9: 696 + 87 = 783
Step 10: 783 + 87 = 870
Step 11: 870 + 87 = 957
Step 12: 957 + 87 = 1044
Step 13: 1044 + 87 = 1131
Step 14: 1131 + 87 = 1218
Step 15: 1218 + 87 = 1305

So, 87*15 = 1305