Answer
$\phi=-750\frac{N.m^2}{C}$
Work Step by Step
According to Gauss's law, the flux through any closed surface is given as $\phi=\frac{q}{\epsilon_{\circ}}$.
It is clear from the above equation that flux does not depend on radius of the sphere, hence the flux will remain same even if the radius is doubled that is $\phi=-750\frac{N.m^2}{C}$.
