Alright, let's solve this math problem step by step. First, we have the number 138. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 31. So, we're going to take the number 138 and add it to itself 31 times.
Step 1: 0 + 138 = 138
Step 2: 138 + 138 = 276
Step 3: 276 + 138 = 414
Step 4: 414 + 138 = 552
Step 5: 552 + 138 = 690
Step 6: 690 + 138 = 828
Step 7: 828 + 138 = 966
Step 8: 966 + 138 = 1104
Step 9: 1104 + 138 = 1242
Step 10: 1242 + 138 = 1380
Step 11: 1380 + 138 = 1518
Step 12: 1518 + 138 = 1656
Step 13: 1656 + 138 = 1794
Step 14: 1794 + 138 = 1932
Step 15: 1932 + 138 = 2070
Step 16: 2070 + 138 = 2208
Step 17: 2208 + 138 = 2346
Step 18: 2346 + 138 = 2484
Step 19: 2484 + 138 = 2622
Step 20: 2622 + 138 = 2760
Step 21: 2760 + 138 = 2898
Step 22: 2898 + 138 = 3036
Step 23: 3036 + 138 = 3174
Step 24: 3174 + 138 = 3312
Step 25: 3312 + 138 = 3450
Step 26: 3450 + 138 = 3588
Step 27: 3588 + 138 = 3726
Step 28: 3726 + 138 = 3864
Step 29: 3864 + 138 = 4002
Step 30: 4002 + 138 = 4140
Step 31: 4140 + 138 = 4278

So, 138*31 = 4278