The sum of the interior angles of a regular polygon with $k$ sides is given as $(3k - 10)$ right angles. We need to find the size of the exterior angle of the polygon.

1. Problem Description

The sum of the interior angles of a regular polygon with $k$ sides is given as $(3k - 10)$ right angles. We need to find the size of the exterior angle of the polygon.

2. Solution Steps

First, we need to convert the given sum of interior angles from right angles to degrees. Since one right angle is 90 degrees, the sum of the interior angles in degrees is $(3k - 10) \times 90$.

The formula for the sum of interior angles of a polygon with $k$ sides is:

$$(k-2) \times 180$$

Equating the two expressions for the sum of interior angles, we have:

$$(k-2) \times 180 = (3k - 10) \times 90$$

Divide both sides by 90:

$$(k-2) \times 2 = 3k - 10$$

$$2k - 4 = 3k - 10$$

$$3k - 2k = 10 - 4$$

$$k = 6$$

So the polygon has 6 sides (a hexagon). Since the polygon is regular, all its interior angles are equal.

The measure of each interior angle is given by the formula:

$$\frac{(k-2) \times 180}{k} = \frac{(6-2) \times 180}{6} = \frac{4 \times 180}{6} = \frac{720}{6} = 120$$

So, each interior angle measures 120 degrees.

The exterior angle and the interior angle are supplementary, meaning they add up to 180 degrees. Therefore, the exterior angle is:

$$180 - 120 = 60$$

3. Final Answer

The size of the exterior angle is 60 degrees.

The answer is A. 60°.