A 1.4-µC point charge is placed between the plates of a parallel plate capacitor.?

A 1.4-µC point charge is placed between the plates of a parallel plate capacitor. The charge experiences a force of 0.72 N. What is the magnitude σ of the charge density on either plate of the capacitor?

I'm trying to study for my test and my book is online and I cant seem to find the answers anywhere. I just want to make sure I am doing this right before my test. PLEASE HELP.