OK, let's work through this together. We're starting with 55 and we're going to multiply it by 15, which means we add 55 to itself 15 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

So, 55*15 = 825