Solve the Equation: Finding the Missing Number in 2200 - □ = 2100

To solve this problem, we need to find the number that, when subtracted from 2200, results in 2100. Let's follow these steps:

• Step 1: Recognize that we are solving for the missing number, denoted by $\Box$, in the equation $2200 - \Box = 2100$.
• Step 2: Rearrange the equation to solve for $\Box$. The equation can be rewritten as $\Box = 2200 - 2100$.
• Step 3: Perform the subtraction to find $\Box$. Calculate 2200 minus 2100.

Calculating the subtraction:

$2200 - 2100 = 100$

Therefore, the missing number, $\Box$, is 100.

In conclusion, the correct answer is $100$.