OK, let's work through this together. We're starting with 911 and we're going to multiply it by 15, which means we add 911 to itself 15 times.
Step 1: 0 + 911 = 911
Step 2: 911 + 911 = 1822
Step 3: 1822 + 911 = 2733
Step 4: 2733 + 911 = 3644
Step 5: 3644 + 911 = 4555
Step 6: 4555 + 911 = 5466
Step 7: 5466 + 911 = 6377
Step 8: 6377 + 911 = 7288
Step 9: 7288 + 911 = 8199
Step 10: 8199 + 911 = 9110
Step 11: 9110 + 911 = 10021
Step 12: 10021 + 911 = 10932
Step 13: 10932 + 911 = 11843
Step 14: 11843 + 911 = 12754
Step 15: 12754 + 911 = 13665

So, 911*15 = 13665