OK, let's crack this. We're given 168 and our task is to multiply it by 15. Essentially, we'll be adding 168 to itself 15 times.
Step 1: 0 + 168 = 168
Step 2: 168 + 168 = 336
Step 3: 336 + 168 = 504
Step 4: 504 + 168 = 672
Step 5: 672 + 168 = 840
Step 6: 840 + 168 = 1008
Step 7: 1008 + 168 = 1176
Step 8: 1176 + 168 = 1344
Step 9: 1344 + 168 = 1512
Step 10: 1512 + 168 = 1680
Step 11: 1680 + 168 = 1848
Step 12: 1848 + 168 = 2016
Step 13: 2016 + 168 = 2184
Step 14: 2184 + 168 = 2352
Step 15: 2352 + 168 = 2520

So, 168*15 = 2520