You need to make some assumptions and just put up formulas
assume that the lateral height of the cone=l=
and assume that the base radius of the cone is r
so you have, V=
then you have C.S.A. OF A CONE =
and a good hint is that you should use the formula of l as given above in the formula of the csa of the cone.
i hope this helps you:)
feel free to ask any querries:)