Question 338080
Given AD is perpendicular to FB, you know 
(angle4 + angle3 = 90)
(angle1 + angle2 = 90)

So then
90 = 90
(angle4 + angle3 = angle1 + angle 2)
You are told angle3 = angle1
thus
(angle4 + angle1 = angle1 + angle2)
(angle4 = angle2)