[tex]V= \frac{1}{3} \pi r^{2} h[/tex]
[tex]r= \frac{d}{2} = \frac{21}{2} = 10.5[/tex]
h=4
Now plug those in to the formula.
[tex]V= \frac{1}{3} (3.14) [tex] (10.5)^{2} [/tex]4[/tex]
Let's work on the multiplication first, then we will do the fraction.
[tex] 10.5^{2} [/tex] = 110.25*3.14 = 346.185 * 4 = 1384.74
So now we have [tex]V= \frac{1}{3} (1384.74) = 461.58[/tex]
Hope that helps.