How can I find the electric field above an infinite sheet?

[hockey]

Homework Statement

A square insulating sheet 75.0cm on a side is held horizontally. The sheet has 7.40nC of charge spread uniformly over its area. Calculate the electric field at a point 0.240mm above the center of the sheet.

Homework Equations

\Phi = 2EA
E = \sigma / 2\epsilon

The Attempt at a Solution

With the formulas above I managed to find that \sigma = 1.316 * 10^-8, but I do not know that \epsilon represents or how to find it. I cannot find the electric field until epsilon has been found.

 

[nrqed]

Homework Statement

A square insulating sheet 75.0cm on a side is held horizontally. The sheet has 7.40nC of charge spread uniformly over its area. Calculate the electric field at a point 0.240mm above the center of the sheet.

Homework Equations

\Phi = 2EA
E = \sigma / 2\epsilon

The Attempt at a Solution

With the formulas above I managed to find that \sigma = 1.316 * 10^-8, but I do not know that \epsilon represents or how to find it. I cannot find the electric field until epsilon has been found.

\epsilon is the dielectric constant of vacuum (usually written as $\epsilon_0$ ). It is a constant that you can look up.