The figure shows two long, parallel current$-$carrying wires. The currents are $I_1=4\mathrm{.}0$A and $I_2=9\mathrm{.}0A$ in the directions indicated. $I_1$ crosses the y $-$axis at $y=+6cm$ and $I_2$ crosses the $y-$axis at $y=-6cm.$

a$.[10$ points$]$ Calculate the magnitude and direction of the net magnetic field at the point $P$ on the x $-$axis at $x=8cm.$

b$.[8$ points$]$ If a proton arrives at the origin with a speed of ${10}^7\frac{m}{s}$ moving in the $+$z direction, what would be the magnitude and direction of the force on this proton when it is at the origin?