Let's roll up our sleeves and solve this. We have 91 and we're going to multiply it by 10, essentially adding 91 to itself 10 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

So, 91*10 = 910