Solve the following equations: 7 + 2 = ?, 7 + ? = 9, ? + 2 = 9.

$$7 + 2 = \square$$ $$7 + 2 = 9$$

The missing number is 9.

$$\boxed{9}$$

$$7 + \square = 9$$

To find the missing number, subtract 7 from 9.

$$\square = 9 - 7$$ $$\square = 2$$

The missing number is 2.

$$\boxed{2}$$

$$\square + 2 = 9$$

To find the missing number, subtract 2 from 9.

$$\square = 9 - 2$$ $$\square = 7$$

The missing number is 7.

$$\boxed{7}$$