Sure thing, let's get straight to it. We start with 55 and we're going to multiply it by 21, which means adding 55 to itself 21 times.
Step 1: 0 + 55 = 55
Step 2: 55 + 55 = 110
Step 3: 110 + 55 = 165
Step 4: 165 + 55 = 220
Step 5: 220 + 55 = 275
Step 6: 275 + 55 = 330
Step 7: 330 + 55 = 385
Step 8: 385 + 55 = 440
Step 9: 440 + 55 = 495
Step 10: 495 + 55 = 550
Step 11: 550 + 55 = 605
Step 12: 605 + 55 = 660
Step 13: 660 + 55 = 715
Step 14: 715 + 55 = 770
Step 15: 770 + 55 = 825
Step 16: 825 + 55 = 880
Step 17: 880 + 55 = 935
Step 18: 935 + 55 = 990
Step 19: 990 + 55 = 1045
Step 20: 1045 + 55 = 1100
Step 21: 1100 + 55 = 1155

So, 55*21 = 1155