Question

If a regular polygon has 40 sides the measure of each interior angle will be

Answer 1

The formula for interior angles is:

$S=180(n-2) n=number of sides s=sum of interior angles.$

Using this, plug in 40 as n and find s.
If you do that, you will get s=6840.
Now that you have the sum of interior angles, you have to find one single measure of an angle in your regular polygon. 
If 40 equal sides in a regular polygon results to 6,840°, then one vertex should be the sum of the interior angles divided by the total number of sides.

In other words, you will have to find 6840°/40. You will get 171°.  That means that the measure of a single interior angle is 171*.

Answer 2

Each exterior angle  = 360 / 40  = 9 degrees. So each interior angle = 180 - 9
 = 171 degrees.