Current Attempt in Progress

Three forces are applied to an object, as shown in the figure. Force vec$(F_1)$ has a magnitude of $21\mathrm{.}3$ newtons $(21\mathrm{.}3N)$ and is directed $30\mathrm{.}0$ to the left of the $+y$ axis. Force vec$(F_2)$ has a magnitude of $15\mathrm{.}7N$ and points along the $+x$ axis. What must be the $($a$)$ magnitude and $($b$)$ direction $($specified by the angle $$ in the drawing$)$ of the third force vec$(F_3)$ such that the vector sum of the three forces is $ON?$