Velocity of a plane when you hear a sonic boom?

[KoontzyN]

Homework Statement

A plane flies directly over your head. When the plane is 45° above the horizon from your perspective, you hear a sonic boom. How fast is the plane flying?

Homework Equations

Doppler effect for a receding source
f_- = f_o / (1+V_source/c)

The Attempt at a Solution

Any help would be appreciated, I'm not sure where to start!

 

[FactChecker]

The doppler shift of the frequency is not relevant. You need to make a triangle diagram of the speeds and do a little trigonometry.