Let's get this math done. We have 715 and we're going to multiply it by 28. This is the same as taking 715 and adding it to itself 28 times.
Step 1: 0 + 715 = 715
Step 2: 715 + 715 = 1430
Step 3: 1430 + 715 = 2145
Step 4: 2145 + 715 = 2860
Step 5: 2860 + 715 = 3575
Step 6: 3575 + 715 = 4290
Step 7: 4290 + 715 = 5005
Step 8: 5005 + 715 = 5720
Step 9: 5720 + 715 = 6435
Step 10: 6435 + 715 = 7150
Step 11: 7150 + 715 = 7865
Step 12: 7865 + 715 = 8580
Step 13: 8580 + 715 = 9295
Step 14: 9295 + 715 = 10010
Step 15: 10010 + 715 = 10725
Step 16: 10725 + 715 = 11440
Step 17: 11440 + 715 = 12155
Step 18: 12155 + 715 = 12870
Step 19: 12870 + 715 = 13585
Step 20: 13585 + 715 = 14300
Step 21: 14300 + 715 = 15015
Step 22: 15015 + 715 = 15730
Step 23: 15730 + 715 = 16445
Step 24: 16445 + 715 = 17160
Step 25: 17160 + 715 = 17875
Step 26: 17875 + 715 = 18590
Step 27: 18590 + 715 = 19305
Step 28: 19305 + 715 = 20020

So, 715*28 = 20020