(c) To minimize the energy, differentiate the result to part (b) with respect to q, and set the derivative equal to zero. Solve for q, in terms of Q and the radii.

I just need to know how to do B, The answer for a is 4.7 m

Hello there. I noticed that the part c, d and e were not calculated. I figured out part A and B already but  am not sure  on what  equations shold be used for part C to calculate Q, W, and DU since the initial equation used /taught is du=q-w.

Can't understand how to get vector r. a=1.43, b=0.915, the total trip required was 1.582 hours, and c =4.60 at 72.8 degree angle. Do I do the pythagorean theorem?