Alright, let's solve this math problem step by step. First, we have the number 31. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 13. So, we're going to take the number 31 and add it to itself 13 times.
Step 1: 0 + 31 = 31
Step 2: 31 + 31 = 62
Step 3: 62 + 31 = 93
Step 4: 93 + 31 = 124
Step 5: 124 + 31 = 155
Step 6: 155 + 31 = 186
Step 7: 186 + 31 = 217
Step 8: 217 + 31 = 248
Step 9: 248 + 31 = 279
Step 10: 279 + 31 = 310
Step 11: 310 + 31 = 341
Step 12: 341 + 31 = 372
Step 13: 372 + 31 = 403

So, 31*13 = 403