Answer
$1.41\times 10^5\;{\rm N/C}\;\hat i $
Work Step by Step
As we can see from the figure below, the net electric field from both spheres is in the right direction.
And since the point between the two spheres is greater than their radius, the electric field of the sphere appears as an electric field of a point charge.
Thus,
$$E_{net}=(E_1+E_2)\hat i=\left[\dfrac{kq_1}{r_1^2}+\dfrac{kq_2}{r_2^2}\right]\hat i$$
where $r_1=r_2=3+1=4$ cm.
$$E_{net} =\left[ \dfrac{(9\times 10^9)(10\times 10^{-9})}{0.04^2}+\dfrac{(9\times 10^9)(15\times 10^{-9})}{0.04^2}\right]\hat i$$
$$E_{net}=(\color{red}{\bf 1.41\times 10^5}\;{\rm N/C})\;\hat i$$
