OK, let's crack this. We're given 672 and our task is to multiply it by 30. Essentially, we'll be adding 672 to itself 30 times.
Step 1: 0 + 672 = 672
Step 2: 672 + 672 = 1344
Step 3: 1344 + 672 = 2016
Step 4: 2016 + 672 = 2688
Step 5: 2688 + 672 = 3360
Step 6: 3360 + 672 = 4032
Step 7: 4032 + 672 = 4704
Step 8: 4704 + 672 = 5376
Step 9: 5376 + 672 = 6048
Step 10: 6048 + 672 = 6720
Step 11: 6720 + 672 = 7392
Step 12: 7392 + 672 = 8064
Step 13: 8064 + 672 = 8736
Step 14: 8736 + 672 = 9408
Step 15: 9408 + 672 = 10080
Step 16: 10080 + 672 = 10752
Step 17: 10752 + 672 = 11424
Step 18: 11424 + 672 = 12096
Step 19: 12096 + 672 = 12768
Step 20: 12768 + 672 = 13440
Step 21: 13440 + 672 = 14112
Step 22: 14112 + 672 = 14784
Step 23: 14784 + 672 = 15456
Step 24: 15456 + 672 = 16128
Step 25: 16128 + 672 = 16800
Step 26: 16800 + 672 = 17472
Step 27: 17472 + 672 = 18144
Step 28: 18144 + 672 = 18816
Step 29: 18816 + 672 = 19488
Step 30: 19488 + 672 = 20160

So, 672*30 = 20160