Sure thing! We've got 6 and we're gonna multiply it by 21. That's the same as adding 6 to itself 21 times.
Step 1: 0 + 6 = 6
Step 2: 6 + 6 = 12
Step 3: 12 + 6 = 18
Step 4: 18 + 6 = 24
Step 5: 24 + 6 = 30
Step 6: 30 + 6 = 36
Step 7: 36 + 6 = 42
Step 8: 42 + 6 = 48
Step 9: 48 + 6 = 54
Step 10: 54 + 6 = 60
Step 11: 60 + 6 = 66
Step 12: 66 + 6 = 72
Step 13: 72 + 6 = 78
Step 14: 78 + 6 = 84
Step 15: 84 + 6 = 90
Step 16: 90 + 6 = 96
Step 17: 96 + 6 = 102
Step 18: 102 + 6 = 108
Step 19: 108 + 6 = 114
Step 20: 114 + 6 = 120
Step 21: 120 + 6 = 126

So, 6*21 = 126