Alright, let's solve this math problem step by step. First, we have the number 805. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 21. So, we're going to take the number 805 and add it 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