Gauss's Law, net electric flux

[yaro99]

Homework Statement

The three small spheres shown in the figure below carry charges q1 = 4.30 nC, q2 = -7.70 nC, and q3 = 3.40 nC.

Find the net electric flux through each of the following closed surfaces shown in cross section in the figure.

Homework Equations

[itex]\Phi[/itex]_E=[itex]\frac{Q_{encl}}{\epsilon_0}[/itex]

The Attempt at a Solution

Using the above equation, I got the right answers for S1 through S4, but I'm getting the wrong answer for S5:
[itex]\Phi[/itex]_E=[itex]\frac{Q_{encl}}{\epsilon_0}[/itex]= [itex]\frac{4.30-7.70+3.40}{\epsilon_0}[/itex]= [itex]\frac{0}{\epsilon_0}[/itex]=0

 

[rude man]

I think your answer is correct.