Question

COULOMB'S LAW

Answer 1

Nice clear problem.

Start with F = K q / r^2

where q will be either -4 NC or +1.5 NC

r will be a or b, in meters, not cm

K is 9 x 10^9

Get the x and y components of the two field vectors, add them

the resulting components are those of the resulting field.

Get its magnitude from the square root of the sum of the squared components.

My answer matched one of the options.