Answer:
Fint = - 67.094 N
Explanation:
Given
W = 71.4 N
∅ = 20º
Fint = ?
The interaction partner of the Normal Force has equal magnitude and opposite direction to the Normal Force, and it is a contact force exerted by the crate on the ramp, because the interaction parteners are the same force acts on the two object.
Then: Fint = - N = - Wy' = - W*Cos ∅
⇒ Fint = - 71.4 N*Cos 20º = - 67.094 N