So the angle BAC is (180-X-X-20) degrees.

And because AF bisects the angle BAC,

So the angle BAF is (180-X-X-20)/2 degrees =(80-X) degrees.

And because the angle b is (X+20) degrees,

So the angle AEB is 180- angle B minus angle BAF= 180-(80-X) degrees -(X+20) degrees =80 degrees.

So CEF angle =80 degrees.

Because the BDF angle is equal to 90 degrees,

So the angle F= 180- angle CEF- angle BDF= 180 degrees -80 degrees -90 degrees = 10 degrees.

Khan, it's awkward to fight.

This is not a difficult question, although it looks troublesome. Do you understand?