Problem $1(20$ points$)$

$+9$

$3$

$+$a

$$ a

$+$a

$+9$

$2$

$+94$

Consider four point charges arranged on the coordinate system above.

$(10$ pts$.)$ Calculate the magnitude and direction of the force a charge of $+$Q would feel at the origin $(0,0).$ Use vector notation.

$(10$ pts$.)$ Calculate the magnitude and direction of the electric field at the point $($O$,$a$)($on the y$-$axis between the charges$).$