Let's get this math done. We have 335 and we're going to multiply it by 21. This is the same as taking 335 and adding it to itself 21 times.
Step 1: 0 + 335 = 335
Step 2: 335 + 335 = 670
Step 3: 670 + 335 = 1005
Step 4: 1005 + 335 = 1340
Step 5: 1340 + 335 = 1675
Step 6: 1675 + 335 = 2010
Step 7: 2010 + 335 = 2345
Step 8: 2345 + 335 = 2680
Step 9: 2680 + 335 = 3015
Step 10: 3015 + 335 = 3350
Step 11: 3350 + 335 = 3685
Step 12: 3685 + 335 = 4020
Step 13: 4020 + 335 = 4355
Step 14: 4355 + 335 = 4690
Step 15: 4690 + 335 = 5025
Step 16: 5025 + 335 = 5360
Step 17: 5360 + 335 = 5695
Step 18: 5695 + 335 = 6030
Step 19: 6030 + 335 = 6365
Step 20: 6365 + 335 = 6700
Step 21: 6700 + 335 = 7035

So, 335*21 = 7035