Alright, let's solve this math problem step by step. First, we have the number 91. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 9. So, we're going to take the number 91 and add it to itself 9 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

So, 91*9 = 819