Perform the operations indicated in each row.

$$98 - 66 = 32$$

The difference is $\boxed{32}$.

(Note: This appears to be an addition problem despite the "Subtraction" heading.)

$$72 + 21 = 93$$

The sum is $\boxed{93}$.

$$20 - 10 = 10$$

The difference is $\boxed{10}$.

$$35 - 15 = 20$$

The difference is $\boxed{20}$.

$$25 - 15 = 10$$

The difference is $\boxed{10}$.

$$80 - 20 = 60$$

The difference is $\boxed{60}$.

$$28 - 15 = 13$$

The difference is $\boxed{13}$.

$$38 - 11 = 27$$

The difference is $\boxed{27}$.

$$99 - 11 = 88$$

The difference is $\boxed{88}$.