Homework help with calculating the electric field from two separate point charges

[deGallo]

Homework Statement

I am having trouble solving this question related to electric field.

Relevant Equations

I used k(q1/a^2 +q2/b^2) a=4.24 b=4 q1=1.6e-6 q2=2.4e-6
The answer I got is 2149 N/C (wrong)

 

[TSny]

Hint: Electric field is a vector quantity.

 

[haruspex]

To illustrate @TSny's point, if the charges had been $q_1=9\mu C, q_2=-1\mu C$, your calculation would have said the field is zero.