Sorry for the ambiguity, the question just asks to compute the magnitude and direction of the proton as observed in S'.
I worked more on the problem and completed the x and y components.
Using the velocity transformations, the x-component was 0.85c*cos(50), doing the calculation out with...
1. A cosmic-ray proton streaks through the lab with velocity 0.85c at an angle of 50o with the +x direction (in the xy plane of the lab). Compute the magnitude and direction of the proton’s velocity when viewed from frame S’ moving with β=0.72 in the +x direction.
2. Ux'= Ux-v/1-vUx/c^2...