Electrostatics - Medium

Figure shows five charged lumps of non-conducting material. The cross-section of a Gaussian surface

S

is indicated. What is the net electric flux through the surface if

q_1 = q_4 = 10\,\text{nC}

q_2 = q_5 = -10\,\text{nC}

and

q_3 = -5\,\text{nC}