Alright, let's solve this math problem step by step. First, we have the number 810. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 27. So, we're going to take the number 810 and add it to itself 27 times.
Step 1: 0 + 810 = 810
Step 2: 810 + 810 = 1620
Step 3: 1620 + 810 = 2430
Step 4: 2430 + 810 = 3240
Step 5: 3240 + 810 = 4050
Step 6: 4050 + 810 = 4860
Step 7: 4860 + 810 = 5670
Step 8: 5670 + 810 = 6480
Step 9: 6480 + 810 = 7290
Step 10: 7290 + 810 = 8100
Step 11: 8100 + 810 = 8910
Step 12: 8910 + 810 = 9720
Step 13: 9720 + 810 = 10530
Step 14: 10530 + 810 = 11340
Step 15: 11340 + 810 = 12150
Step 16: 12150 + 810 = 12960
Step 17: 12960 + 810 = 13770
Step 18: 13770 + 810 = 14580
Step 19: 14580 + 810 = 15390
Step 20: 15390 + 810 = 16200
Step 21: 16200 + 810 = 17010
Step 22: 17010 + 810 = 17820
Step 23: 17820 + 810 = 18630
Step 24: 18630 + 810 = 19440
Step 25: 19440 + 810 = 20250
Step 26: 20250 + 810 = 21060
Step 27: 21060 + 810 = 21870

So, 810*27 = 21870