Step 1: Write the second number under the first number so that the ones, tens, and hundreds places are lined up.

Step 2: Add the ones column (3 + 4 = 7). Write the 7 in the ones place of the sum.

Step 3: Add the tens column (5 + 7 = 12).
12 has two digits, but both digits will not fit in the tens place. So, write the 2 in the tens place of the sum, and carry the 1 to the hundreds column. This is called regrouping.

Step 4: Add the hundreds column (1 + 2 + 1 = 4). Write the 4 in the hundreds place of the sum.