Two very large sheets are 5cm apart. Sheet A carries a uniform surface density of -9.70 muC/m^2 and sheet B, which is to the right of A, carries a uniform charge of -12.1 muC/m^2. Assume the sheets are large enough to be treated as infinite.

A. Find the magnitude of the net electric field these sheets produce at a point 4cm to the right of sheet A.
B. Find the magnitude of the net electric field these sheets produce at a point 4cm to the left of sheet A.
C. Find the magnitude of the net electric field these sheets produce at a point 4cm to the right of sheet B.
D. Find the magnitude of the net electric field these sheets produce at a point 4cm to the left of sheet B.

Answers need to be N/C.
I know the formula to be used for Part A is :
(-|gamma_A| + |gamma_B|) / 2*epsilon_0
using, r=4, this gives me an answer of 2711 N/m.

How do I turn this into N/C, and is r=4 correct?

ANY help is greatly appreciated!