Sure thing, let's get straight to it. We start with 805 and we're going to multiply it by 21, which means adding 805 to itself 21 times.
Step 1: 0 + 805 = 805
Step 2: 805 + 805 = 1610
Step 3: 1610 + 805 = 2415
Step 4: 2415 + 805 = 3220
Step 5: 3220 + 805 = 4025
Step 6: 4025 + 805 = 4830
Step 7: 4830 + 805 = 5635
Step 8: 5635 + 805 = 6440
Step 9: 6440 + 805 = 7245
Step 10: 7245 + 805 = 8050
Step 11: 8050 + 805 = 8855
Step 12: 8855 + 805 = 9660
Step 13: 9660 + 805 = 10465
Step 14: 10465 + 805 = 11270
Step 15: 11270 + 805 = 12075
Step 16: 12075 + 805 = 12880
Step 17: 12880 + 805 = 13685
Step 18: 13685 + 805 = 14490
Step 19: 14490 + 805 = 15295
Step 20: 15295 + 805 = 16100
Step 21: 16100 + 805 = 16905

So, 805*21 = 16905