Let's get this math done. We have 642 and we're going to multiply it by 28. This is the same as taking 642 and adding it to itself 28 times.
Step 1: 0 + 642 = 642
Step 2: 642 + 642 = 1284
Step 3: 1284 + 642 = 1926
Step 4: 1926 + 642 = 2568
Step 5: 2568 + 642 = 3210
Step 6: 3210 + 642 = 3852
Step 7: 3852 + 642 = 4494
Step 8: 4494 + 642 = 5136
Step 9: 5136 + 642 = 5778
Step 10: 5778 + 642 = 6420
Step 11: 6420 + 642 = 7062
Step 12: 7062 + 642 = 7704
Step 13: 7704 + 642 = 8346
Step 14: 8346 + 642 = 8988
Step 15: 8988 + 642 = 9630
Step 16: 9630 + 642 = 10272
Step 17: 10272 + 642 = 10914
Step 18: 10914 + 642 = 11556
Step 19: 11556 + 642 = 12198
Step 20: 12198 + 642 = 12840
Step 21: 12840 + 642 = 13482
Step 22: 13482 + 642 = 14124
Step 23: 14124 + 642 = 14766
Step 24: 14766 + 642 = 15408
Step 25: 15408 + 642 = 16050
Step 26: 16050 + 642 = 16692
Step 27: 16692 + 642 = 17334
Step 28: 17334 + 642 = 17976

So, 642*28 = 17976