Question

find the measure of the missing angle. 42°

Explanation:

Step1: Assume it's a right - angle problem

Assume the whole angle is a right - angle of 90°.

Step2: Calculate the missing angle

Let the missing angle be $x$. Then $x = 90^{\circ}-42^{\circ}$.
$x = 48^{\circ}$

Answer:

$48^{\circ}$