Let's get this math done. We have 348 and we're going to multiply it by 21. This is the same as taking 348 and adding it to itself 21 times.
Step 1: 0 + 348 = 348
Step 2: 348 + 348 = 696
Step 3: 696 + 348 = 1044
Step 4: 1044 + 348 = 1392
Step 5: 1392 + 348 = 1740
Step 6: 1740 + 348 = 2088
Step 7: 2088 + 348 = 2436
Step 8: 2436 + 348 = 2784
Step 9: 2784 + 348 = 3132
Step 10: 3132 + 348 = 3480
Step 11: 3480 + 348 = 3828
Step 12: 3828 + 348 = 4176
Step 13: 4176 + 348 = 4524
Step 14: 4524 + 348 = 4872
Step 15: 4872 + 348 = 5220
Step 16: 5220 + 348 = 5568
Step 17: 5568 + 348 = 5916
Step 18: 5916 + 348 = 6264
Step 19: 6264 + 348 = 6612
Step 20: 6612 + 348 = 6960
Step 21: 6960 + 348 = 7308

So, 348*21 = 7308