Electric field magnitude midway between 2 charges

[astru025]

Homework Statement

What is the electric field magnitude midway between charges of Q1 = 1 C and Q2 = 11 C separated by 2 m?

Homework Equations

E= k (Q/r^2).

The Attempt at a Solution

9E9 x 1C / 1^2 = 9E9 N/C
9E9 x 2C / 1^2= 1.8E10 N/C.

What do I do from here? Any help would be much appreciated thanks!

 

[astru025]

Would the answer be to add my two final values? I would have 2.7E10 N/C as my final answer... Does this look right?

 

[astru025]

That answer above proves to be not correct. What needs to be changed?!