A force F(x) = (-4.0x^2 + 6.0x) N acts on a particle. (a) How much work (in J) does the force do on the particle as it moves from x = 2.0 m to x = 4.0 m? (b) Picking a convenient reference point of the potential energy to be zero at x = 0, find the potential energy for this force. (Use the following as necessary: x. Assume U(x) is in joules and x is in meters. Do not include units in your answer.)