Find the missing digit in each of the following numbers to make them divisible by 11: a) 27...3, b) 1...574, c) 939...?

Since $x$ is a single digit (0-9), the only multiple of 11 possible for $8-x$ is 0.

$$8 - x = 0$$ $$x = 8$$

The number is 2783.

$$\boxed{\text{8}}$$

Since $x$ is a single digit (0-9), the only multiple of 11 possible for $3-x$ is 0.

$$3 - x = 0$$ $$x = 3$$

The number is 13574.

$$\boxed{\text{3}}$$

Since $x$ is a single digit (0-9), the only multiple of 11 possible for $x-15$ is -11.

$$x - 15 = -11$$ $$x = 15 - 11$$ $$x = 4$$

The number is 9394.

$$\boxed{\text{4}}$$

Since $x$ is a single digit (0-9), the only multiple of 11 possible for $4-x$ is 0.

$$4 - x = 0$$ $$x = 4$$

The number is 1045.

$$\boxed{\text{4}}$$