Finding the magnitude of an electric field.

[atn9200]

Homework Statement

Determine the magnitude of the electric field at a point midway between a -8.1μC and a 8.9μC charge 8.0cm apart. Assume no other charges are nearby.
Determine the direction.
(Answer in two sig figs.)

Homework Equations

E=k/r^2(Q1+Q2)

The Attempt at a Solution

I drew this: -8.1---------p----------8.9

This is what I think I'm supposed to do.

The field due to -8.1 charge points toward it.
The field due to 8.9 points away. So they are both pointing towards the negative charge?

so E=k/.08^2(8.1e-6+8.9e-6)=2.4e7 N/C but this is incorrect. Please explain why! Thanks.

 

[atn9200]

I want to slap myself now...is it because r=.04m? Want assurance because I'm on my last strike.