Find the missing number (addition and subtraction within 1000)

The  exercise appears under the 3rd grade (U.S.) Math Mission. This exercise has the user find the number which makes the subtraction statement true.

Types of problems
There is one type of problem in this exercise:
 * 1) Make the statement true: This problem gives the user a subtraction problem in which they need to find the missing number which satisfies the equation.

Strategies
Knowledge of addition and subtraction is required for this exercise.
 * 1) You can usually find the answer by doing an easier addition/subtraction problem involving the two given numbers.

Real-life Applications

 * 1) Addition and subtraction are used in money, as in totaling and deducting.