Determine angle and magnitude of resultant force

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Determine the angle of theata for connecting member A to the plate so that the resultant force of Fa and Fb is directed horizontally to the right. also what is the magnitude of Fr?

I know the answers
a)54.9
b)10.4 kN

I need an explanation, i feel like something is missing from the problem

Fa is to the right and upward. Fb is to the right and downward. Both forces have a horizontal component and a vertical component. You want to choose theta such that Fa's vertical component has the exact magnitude (albeit in the opposite direction) as the vertical component of Fb. When you do that, the net vertical force will be zero. Then the only force will be the sum of their horizontal components.

for the vertical component, we want:
6kN cos(40) = 8kN cos(theta), hence:
theta = arccos(0.75cos(40) = 54.9 degrees

now you know theta, so you can straightaway calculate the resultant horizontal force
Fr = 6kN sin(40) + 8kN sin(theta) = 10.4kN
(I keep the previously calculated full value of theta in my calculator and work with it to find Fr rather than the rounded number since sometimes making subsequent calculations with rounded intermediate answers can give slightly different results.)