Answer: 
Step-by-step explanation:
By definition, the sum of the interior angles of a triangle is 180 degrees.
Based on this, you need to set up the following equation:

The next steo is to solve for "x" in order to find its value. This is:

You can observe in the picture of the triangle ABC given in the exercise, that:

Therefore, you must substitute the value of "x" into that equation and then evaluate, in order to find the measure of the angle B. This is:
