OK, let's crack this. We're given 769 and our task is to multiply it by 21. Essentially, we'll be adding 769 to itself 21 times.
Step 1: 0 + 769 = 769
Step 2: 769 + 769 = 1538
Step 3: 1538 + 769 = 2307
Step 4: 2307 + 769 = 3076
Step 5: 3076 + 769 = 3845
Step 6: 3845 + 769 = 4614
Step 7: 4614 + 769 = 5383
Step 8: 5383 + 769 = 6152
Step 9: 6152 + 769 = 6921
Step 10: 6921 + 769 = 7690
Step 11: 7690 + 769 = 8459
Step 12: 8459 + 769 = 9228
Step 13: 9228 + 769 = 9997
Step 14: 9997 + 769 = 10766
Step 15: 10766 + 769 = 11535
Step 16: 11535 + 769 = 12304
Step 17: 12304 + 769 = 13073
Step 18: 13073 + 769 = 13842
Step 19: 13842 + 769 = 14611
Step 20: 14611 + 769 = 15380
Step 21: 15380 + 769 = 16149

So, 769*21 = 16149