Hi,

You need to know the area of a circle is $\pi \; r^2$ square meters if the radius is $r$ meters and the volume of a cone is $\pi \; r^2 h$ cubic meters if the radius of the base is $r$ meters and the cone is $h$ meters high.

If each person needs 4 square meters of space on the ground then the area of the base must be $4 \times 11 = 44$ square meters. If the area of a circle is 44 square meters what is the radius?

If each person needs 20 cubic meters of air then the cone must have a volume of at least $20 \times 11$ cubic meters. You know the radius of the base so what does the height need to be?

Penny