Four long, parallel wires are located at the corners of a square of side $a=30cm,$ as shown in the figure above, where $I_1=11A,I_2=3A,I_3=6A,I_4=4A.$ Find:

a$)$ the resultant magnetic field at the center of the square:

hat$(i)+$ hat$(k).$

b$)$ the force on an electron moving at $6{10}^6$hat$(i)\frac{m}{s}$ as it passes the center: