Originally Posted by

**masters** Hi Mathaticaln00b,

$\displaystyle V=\frac{\pi h(3r^2+h^2)}{6}$

Substitute what you know...V=15, h=2.54...

$\displaystyle 15=\frac{\pi(2.54)(3r^2+(2.54)^2)}{6}$

Apply the distributive property...

$\displaystyle 15=\frac{7.62 \pi r^2+16.387064 \pi}{6}$

Clear the fraction (Multiply both sides by 6)...

$\displaystyle 90=7.62 \pi r^2+16.387064$

Subtract 16.387064 from both sides...

$\displaystyle 73.612936=7.62\pi r^2$

Divide both sides by $\displaystyle 7.62 \pi$...

$\displaystyle \frac{73.612936}{7.62\pi}=r^2$

Take the square root of both sides...

$\displaystyle \sqrt{\frac{73.612936}{7.62\pi}}=r$