Which point can be used to find f(3)

Commonly the horizontal axis represent the x-axis. So, you need the point that means x = 3 (positive 3), so, it is the point A.

answer is x<

m∠5 + m∠3 = m∠1   is true.

m∠5 + m∠6 = 180 is true

m∠2 +m∠3 = m∠6   is true

m∠2 +m∠3 +m∠5 = 180   is true