Chapter 5, Problem 32PQ

If the vector components of the position of a particle moving in the xy plane as a function of time are $\stackrel{\to }{x}\text{(}t\text{)}=\left(2.5\frac{\text{m}}{{\text{s}}^{\text{2}}}\right)t^{\text{2}}\hat{i}$ and $\stackrel{\to }{y}\text{(}t\text{)}=\left(5.0\frac{\text{m}}{{\text{s}}^{\text{3}}}\right)t^{\text{3}}\hat{j}$, when is the angle between the net force on the particle and the x axis equal to 45°?