My solution is this:
$$q = \varepsilon_0 \int E.dA$$
Based on gauss's law.
Taking the derivative of both sides with respect to $$A$$ we get:
$$\frac{dq}{dA} = \varepsilon_0 E$$
From chain rule:
$$\frac{dq}{dA} = \frac{\frac{dq}{dr}}{\frac{dA}{dr}}$$
On the other hand:
$$q = \int \rho dv = \int...