Sure thing, let's get straight to it. We start with 834 and we're going to multiply it by 21, which means adding 834 to itself 21 times.
Step 1: 0 + 834 = 834
Step 2: 834 + 834 = 1668
Step 3: 1668 + 834 = 2502
Step 4: 2502 + 834 = 3336
Step 5: 3336 + 834 = 4170
Step 6: 4170 + 834 = 5004
Step 7: 5004 + 834 = 5838
Step 8: 5838 + 834 = 6672
Step 9: 6672 + 834 = 7506
Step 10: 7506 + 834 = 8340
Step 11: 8340 + 834 = 9174
Step 12: 9174 + 834 = 10008
Step 13: 10008 + 834 = 10842
Step 14: 10842 + 834 = 11676
Step 15: 11676 + 834 = 12510
Step 16: 12510 + 834 = 13344
Step 17: 13344 + 834 = 14178
Step 18: 14178 + 834 = 15012
Step 19: 15012 + 834 = 15846
Step 20: 15846 + 834 = 16680
Step 21: 16680 + 834 = 17514

So, 834*21 = 17514