Sure thing, let's get straight to it. We start with 664 and we're going to multiply it by 15, which means adding 664 to itself 15 times.
Step 1: 0 + 664 = 664
Step 2: 664 + 664 = 1328
Step 3: 1328 + 664 = 1992
Step 4: 1992 + 664 = 2656
Step 5: 2656 + 664 = 3320
Step 6: 3320 + 664 = 3984
Step 7: 3984 + 664 = 4648
Step 8: 4648 + 664 = 5312
Step 9: 5312 + 664 = 5976
Step 10: 5976 + 664 = 6640
Step 11: 6640 + 664 = 7304
Step 12: 7304 + 664 = 7968
Step 13: 7968 + 664 = 8632
Step 14: 8632 + 664 = 9296
Step 15: 9296 + 664 = 9960

So, 664*15 = 9960