Finding mass of black hole once given the density

[fifel85]

Homework Statement

Calculate the mass and radius of a black hole with density 750 kg/m^3.

Homework Equations

The Attempt at a Solution

In a previous question, I already used the Schwarzschild radius to come up with a formula for the density of a black hole:
D = (mass/(4/3pi((2Gmass/c^2)^3). I realize that this should be enough to solve for mass, but I am having difficulty with the algebra...How do I solve for mass when one of the "mass" variables is stuck inside the Scharzchild radius in a complicated fraction?

 

[George Jones]

Apply the ^3 to everything inside the brackets to which it is attached.