OK, let's work through this together. We're starting with 813 and we're going to multiply it by 28, which means we add 813 to itself 28 times.
Step 1: 0 + 813 = 813
Step 2: 813 + 813 = 1626
Step 3: 1626 + 813 = 2439
Step 4: 2439 + 813 = 3252
Step 5: 3252 + 813 = 4065
Step 6: 4065 + 813 = 4878
Step 7: 4878 + 813 = 5691
Step 8: 5691 + 813 = 6504
Step 9: 6504 + 813 = 7317
Step 10: 7317 + 813 = 8130
Step 11: 8130 + 813 = 8943
Step 12: 8943 + 813 = 9756
Step 13: 9756 + 813 = 10569
Step 14: 10569 + 813 = 11382
Step 15: 11382 + 813 = 12195
Step 16: 12195 + 813 = 13008
Step 17: 13008 + 813 = 13821
Step 18: 13821 + 813 = 14634
Step 19: 14634 + 813 = 15447
Step 20: 15447 + 813 = 16260
Step 21: 16260 + 813 = 17073
Step 22: 17073 + 813 = 17886
Step 23: 17886 + 813 = 18699
Step 24: 18699 + 813 = 19512
Step 25: 19512 + 813 = 20325
Step 26: 20325 + 813 = 21138
Step 27: 21138 + 813 = 21951
Step 28: 21951 + 813 = 22764

So, 813*28 = 22764