Please help me out with this question fasttt. My homework is due in an hour, the answer is not 0 or 112.9. Thanks!!!

A 20 kg helium balloon in the atmosphere has been charged during a thunderstorm. The balloon is spherical with a radius of 25 m. The charge density of the surface of the balloon is s(,)=109 cos()s(,)=109 cos() coulombs-m^-2. Assume the center of the balloon is at the coordinate system origin. Find the z-component of the electric field in the middle of the balloon. Answer in units of V/m.