Without delay, let's solve this. We've got 671 and we will be multiplying it by 15, that is, adding 671 to itself 15 times.
Step 1: 0 + 671 = 671
Step 2: 671 + 671 = 1342
Step 3: 1342 + 671 = 2013
Step 4: 2013 + 671 = 2684
Step 5: 2684 + 671 = 3355
Step 6: 3355 + 671 = 4026
Step 7: 4026 + 671 = 4697
Step 8: 4697 + 671 = 5368
Step 9: 5368 + 671 = 6039
Step 10: 6039 + 671 = 6710
Step 11: 6710 + 671 = 7381
Step 12: 7381 + 671 = 8052
Step 13: 8052 + 671 = 8723
Step 14: 8723 + 671 = 9394
Step 15: 9394 + 671 = 10065

So, 671*15 = 10065