OK, let's work through this together. We're starting with 47 and we're going to multiply it by 21, which means we add 47 to itself 21 times.
Step 1: 0 + 47 = 47
Step 2: 47 + 47 = 94
Step 3: 94 + 47 = 141
Step 4: 141 + 47 = 188
Step 5: 188 + 47 = 235
Step 6: 235 + 47 = 282
Step 7: 282 + 47 = 329
Step 8: 329 + 47 = 376
Step 9: 376 + 47 = 423
Step 10: 423 + 47 = 470
Step 11: 470 + 47 = 517
Step 12: 517 + 47 = 564
Step 13: 564 + 47 = 611
Step 14: 611 + 47 = 658
Step 15: 658 + 47 = 705
Step 16: 705 + 47 = 752
Step 17: 752 + 47 = 799
Step 18: 799 + 47 = 846
Step 19: 846 + 47 = 893
Step 20: 893 + 47 = 940
Step 21: 940 + 47 = 987

So, 47*21 = 987