Sure thing, let's get straight to it. We start with 31 and we're going to multiply it by 13, which means adding 31 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