mechanics 1 math

A box of mass 9 kg rests on a slope, which is at an angle of 34° to the horizontal. It is held in place by a
horizontal force of 20 N.
a) By considering the total contact force as a single force, or otherwise, find the size of the total contact force.
b) Given that friction is limiting, find the coefficient of friction between the box and the slope.
(answer C= 92.2, )

i found R = 74.6 and F= 30.3 but the contact force is not correct

Can you upload what you did?

R= 90cos34= 74.6
F= 90sin34-20= 30.3
C= square root of 74.6^2 + 30.3^2

R would be influenced by the 20N horizontal force and why is F (contact force) the difference etc? A sketch really helps.

Its arguably easier to think of it horizontally and vertically, rather than parallel and perpendicular to the plane.

why would R be influenced by 20N?

The 20N are horizontal to the mass, and it must be first converted to parallel to the slope, but even after it the contact force is not what is written in the answer