How do you find length and crosssectional area of a wire given just resistancevolume and resistivity?

Resistance varies directly as length

Resistance varies inversely as cross-sectional area

Hence R varies as L

and R varies as 1/A

Thus R = r(L/A) where r is the coefficient of resistance of the wire. If the wire is of uniform cross section, then A = V/L where V is the volume of the wire. Hence now we have R = r(L/(V/L)) or R = r(L-squared/V) or L-squared = (RxV)/r and so the answer would be L = square-root of (RxV)/r