Sure thing! We've got 143 and we're gonna multiply it by 21. That's the same as adding 143 to itself 21 times.
Step 1: 0 + 143 = 143
Step 2: 143 + 143 = 286
Step 3: 286 + 143 = 429
Step 4: 429 + 143 = 572
Step 5: 572 + 143 = 715
Step 6: 715 + 143 = 858
Step 7: 858 + 143 = 1001
Step 8: 1001 + 143 = 1144
Step 9: 1144 + 143 = 1287
Step 10: 1287 + 143 = 1430
Step 11: 1430 + 143 = 1573
Step 12: 1573 + 143 = 1716
Step 13: 1716 + 143 = 1859
Step 14: 1859 + 143 = 2002
Step 15: 2002 + 143 = 2145
Step 16: 2145 + 143 = 2288
Step 17: 2288 + 143 = 2431
Step 18: 2431 + 143 = 2574
Step 19: 2574 + 143 = 2717
Step 20: 2717 + 143 = 2860
Step 21: 2860 + 143 = 3003

So, 143*21 = 3003