Find force in the strut:

Question

Wall is 20 ft high.
Strut begins 4 ft lower, so the "altitude" of strut is 16 ft.
"Base" of strut from wall to end of strut = 8 ft.
strut is 12 ft on center
There is a wind force against wall = 20 lb/ft ^2

Teacher said find wind force:
w = (12 ft)(20 lb/ft^2 ) = 240 lb/ft
Sum MB ???
then find Rt
Rt(16ft) – (w)(20ft)(10ft) =
Rt (16 ft) - (240 lb/ft)(200 ft^2) =
Rt (16 ft) - 48,000 lb/ft =
Rt = 48,000 lb/ft div by 16 ft
Rt = 3000 lb/ft^2

QUESTION:
need to find cos of angle because
cos Ɵ = Rt/Fs

Do I use the base angle of 63.43 degrees or the top angle of 26.57 where the strut connects to the wall?
using cos 63.43 = 0.447290848
Fs (0.447290848) = 3000 lb/ft^2
Fs = 6707.05 lb/ft^2

Using 27.57 degrees for the top angle,
Fs = 3384.30 lb/ft^2

Is either of these correct for finding the force of the strut?

Thank you.