Let's get this math done. We have 668 and we're going to multiply it by 18. This is the same as taking 668 and adding it to itself 18 times.
Step 1: 0 + 668 = 668
Step 2: 668 + 668 = 1336
Step 3: 1336 + 668 = 2004
Step 4: 2004 + 668 = 2672
Step 5: 2672 + 668 = 3340
Step 6: 3340 + 668 = 4008
Step 7: 4008 + 668 = 4676
Step 8: 4676 + 668 = 5344
Step 9: 5344 + 668 = 6012
Step 10: 6012 + 668 = 6680
Step 11: 6680 + 668 = 7348
Step 12: 7348 + 668 = 8016
Step 13: 8016 + 668 = 8684
Step 14: 8684 + 668 = 9352
Step 15: 9352 + 668 = 10020
Step 16: 10020 + 668 = 10688
Step 17: 10688 + 668 = 11356
Step 18: 11356 + 668 = 12024

So, 668*18 = 12024