Ok so firstly, you need to remember that when a radius is touching a tangent, the angle is always equal to 90°. So x + 57° = 90°. That means your angle is 33°. You have drawn a right angle which is correct so the left triangle's angle is 90° - 33° = 57°. Now because both sides of the triangle is radius, that means c and 57° are equal. That means c = 57°.
