Question 1139265
{{{ V[cyl] = (pi)r^2h }}}

h=20
V={{{320*(pi)}}}

Solving for 2r (= diameter): {{{ 2r = 2*sqrt(V/(pi*h)) = 2 * sqrt(320pi/20pi)
= 2*sqrt(16) = 2*4 = highlight( 8 )}}}ft