Charge density as a function of r

[JJfortherear]

Homework Statement

Sphere of radius R, E_r=E_R(r⁴/R⁴)
Find the volume charge density (ρ_r) as a function of r

Homework Equations

Gauss's law

The Attempt at a Solution

I get that dQ=4πr²ρ_rdr, but have no idea how to solve for ρ

 

[kuruman]

Have you seen the following form of Gauss's Law?

$$\nabla\cdot E = \rho/\epsilon_0$$

 

[fizzynoob]

like kuruman said, its application of gauss's law

Flux = $$\oint$$E (dot) dA = q/e

you found q to be 4πr2ρ, but p = Charge / Volume

but 4πr^2 isn't the volume of a sphere