Answer: 90 degrees
Since this is a regular polygon, you know that each side and angle will the congruent to each other. First, you need to find the sum of all the interior angles with the formula (n-2)⋅180 (n is how many angles the shape has) In this case there are 4 angles so (4-2)⋅180. Once you solve that we get 360 degrees for the sum of all the interior angles. Now that we know that, we can divide by 4 to see how many degrees each angle is. And the answer is 90 degrees.
Hope this helped you!
