Question 872332
r=7, the radius of tank
h=10.5
C = volume capacity of the tank
{{{C=h*pi*r^2}}}
Tank is half full, so {{{v=(1/2)h*pi*r^2}}}
R=10.5 cubic meters per hour, rate of filling;  do <b>not</b> confuse r with R.


Time to fill that v volume part:
{{{R*t=v}}}, letting t be the time in hours.
{{{t=v/R}}}
{{{highlight(t=(1/(2R))h*pi*r^2)}}}


The solution formula is completely in symbols.  Just substitute the known values to find the time t.  Note that as done here, the formula only works for a half-filled cylinder.  You'd need to carefully adjust the solution steps if other than half-filled.