Answer
$E = 1690~V/m$
Work Step by Step
The electric field inside a spherical shell due to the charge on the outside of the shell is zero.
The electric field outside a spherical shell due to the charge on the outside of the shell is equal to the electric field if all the charge was at the center of the sphere.
We can find the electric field at $r = 4.00~m$:
$E = \frac{1}{4\pi~\epsilon_0}~\frac{q}{r^2}$
$E = \frac{1}{4\pi~\epsilon_0}~\frac{q_1+q_2}{r^2}$
$E = \frac{1}{4\pi~\epsilon_0}~\frac{2.00~\mu C+1.00~\mu C}{r^2}$
$E = \frac{1}{(4\pi)~(8.854\times 10^{-12}~C/V~m)}~\frac{3.00\times 10^{-6}~C}{(4.00~m)^2}$
$E = 1690~V/m$
