Let's get this math done. We have 1391 and 100 and we're going to add them all together.

Step 1: We'll start by adding the digits 1 & 0 in column 1 and get 1.

Step 2: We'll start by adding the digits 9 & 0 in column 2 and get 9.

Step 3: We'll start by adding the digits 3 & 1 in column 3 and get 4.

Step 4: We'll start by adding the digits 1 & 0 in column 4 and get 1.

So, 1391 + 100 = 1491.

