Lesson Steps:

The two numbers have three digits each.
Hundreds digit of 100: 1
Hundreds digit of 200: 2
Tens digit of 100: 0
Tens digit of 200: 0
Ones digit of 100: 0
Ones digit of 200: 0

First, we subtract ones digits.
0 - 0 = 0
Second, we subtract the tens digits.
0 - 0 = 0
Finally, the hundreds digits.
2 - 1 = 1

Combining the hundreds digit, tens digit and ones digit, we get the answer:
100

Answer:

100

Grade: 4
Level: Middle school
Subject: Math
Topic: Addition