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).
Since 12 has two digits, both digits won't 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.

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

Step 2: Look at the ones column. 3 is less than 4, so take 1 ten from the tens place, change the ten to 10 ones, and add the 10 ones to the ones place. This is called regrouping.
Then, subtract the ones column (13 - 4 = 9). Write the 9 in the ones place of the difference.

Step 3: Subtract the tens column (7 - 0 = 7). Write the 7 in the tens place of the difference.

Step 4: Subtract the hundreds column (7 - 4 = 3). Write the 3 in the hundreds place of the difference.