OK, let's work through this together. We're starting with 91 and we're going to multiply it by 13, which means we add 91 to itself 13 times.
Step 1: 0 + 91 = 91
Step 2: 91 + 91 = 182
Step 3: 182 + 91 = 273
Step 4: 273 + 91 = 364
Step 5: 364 + 91 = 455
Step 6: 455 + 91 = 546
Step 7: 546 + 91 = 637
Step 8: 637 + 91 = 728
Step 9: 728 + 91 = 819
Step 10: 819 + 91 = 910
Step 11: 910 + 91 = 1001
Step 12: 1001 + 91 = 1092
Step 13: 1092 + 91 = 1183

So, 91*13 = 1183