Without delay, let's solve this. We've got 153 and we will be multiplying it by 21, that is, adding 153 to itself 21 times.
Step 1: 0 + 153 = 153
Step 2: 153 + 153 = 306
Step 3: 306 + 153 = 459
Step 4: 459 + 153 = 612
Step 5: 612 + 153 = 765
Step 6: 765 + 153 = 918
Step 7: 918 + 153 = 1071
Step 8: 1071 + 153 = 1224
Step 9: 1224 + 153 = 1377
Step 10: 1377 + 153 = 1530
Step 11: 1530 + 153 = 1683
Step 12: 1683 + 153 = 1836
Step 13: 1836 + 153 = 1989
Step 14: 1989 + 153 = 2142
Step 15: 2142 + 153 = 2295
Step 16: 2295 + 153 = 2448
Step 17: 2448 + 153 = 2601
Step 18: 2601 + 153 = 2754
Step 19: 2754 + 153 = 2907
Step 20: 2907 + 153 = 3060
Step 21: 3060 + 153 = 3213

So, 153*21 = 3213