Alright, let's solve this math problem step by step. First, we have the number 6. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 21. So, we're going to take the number 6 and add it 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