the formula to find the total angle measure in an irregular polygon is (n-2)*180 where n is the number of sides it has; In your case, 4, so:
(4-2)*180
2*180
360 total degrees
Since you already know 3 of the angles, just add them all together and subtract that from 180 to find the final angle.
132+79+56=267
360-267=93 degrees for the final unknown angle.