What is the formula for calculating the mass of a star in astronomy?

[Unto]

Homework Statement

...Hence show that the mass of the star is M = $$4\pi$$$$p_{c}$$$$\left(R^{3}/3 )$$

Homework Equations

M(r) = $$4 \pi$$$$p_{c}$$$$\left(r^{3}/3 - r^{4}/4R)$$
This is the shell mass

The Attempt at a Solution

I already found the shell mass via intergration, and I know that I have to build up an 'infinite' number of shells to get the whole mass of the star. But do I use integration or something else? What do I do?

 

[Unto]

Hello? You don't really need to know about Astronomy to answer this question, I'm just really dumb and unsure whether to intergrate to find the mass throughout the star. Please help.

 

[clamtrox]

Is your star supposed to have an even mass distribution? Because your formula for the mass shell seems really weird. For a constant density it should be proportional to r^2.