OK, let's crack this. We're given 364 and our task is to multiply it by 21. Essentially, we'll be adding 364 to itself 21 times.
Step 1: 0 + 364 = 364
Step 2: 364 + 364 = 728
Step 3: 728 + 364 = 1092
Step 4: 1092 + 364 = 1456
Step 5: 1456 + 364 = 1820
Step 6: 1820 + 364 = 2184
Step 7: 2184 + 364 = 2548
Step 8: 2548 + 364 = 2912
Step 9: 2912 + 364 = 3276
Step 10: 3276 + 364 = 3640
Step 11: 3640 + 364 = 4004
Step 12: 4004 + 364 = 4368
Step 13: 4368 + 364 = 4732
Step 14: 4732 + 364 = 5096
Step 15: 5096 + 364 = 5460
Step 16: 5460 + 364 = 5824
Step 17: 5824 + 364 = 6188
Step 18: 6188 + 364 = 6552
Step 19: 6552 + 364 = 6916
Step 20: 6916 + 364 = 7280
Step 21: 7280 + 364 = 7644

So, 364*21 = 7644