Physics question, Please help!?

[steiberdavid]

A friend is working on a biology experiment and needs to create an electric field of magnitude 470 at a distance of 10 from the central portion of a large nonconducting square plate 4.2 on each side. She needs to know how much charge to put on the plate.

What do you tell her?
|Q| = ??? C


A nonconducting square plate 74 on a side carries a uniform surface charge density. The electric field strength 1 from the plate, not near an edge, is 50 .

What is the approximate field strength 23 from the plate?
E= ??? N/C

If you could help me with these questions, that would be awesome. I seem to keep getting close, but when i plug the answers i get, it always comes out wrong... I've been doign them for hours!! PLEASE HELP!
BTW, the 50 is 50 KN/C
Oh, wow. When i copy pasted the problems, i guess the values disappeared. lol
A friend is working on a biology experiment and needs to create an electric field of magnitude 470 N/C at a distance of 10 cm from the central portion of a large nonconducting square plate 4.2 m on each side. She needs to know how much charge to put on the plate.


PS, i got the answer to the other question correct, seems i just made an algebra mistake.

[Jackie]

I would tell her to include units with numbers so we know what exactly she's talking about. Is the magnetic field in Teslas or Gauss's? Is the distance in millimeters or centimeters? Is the area in square centimeters or square meters?