Right option is (a) V = 3.4*(Stop*Aside/4L)
The explanation is: Internal volume of fuselage will be total available volume for crew, cargo, passenger etc. Typically, from side and top view we can estimate internal volume. If area of side is Aside and area of top is Stop then, internal volume is given as, V = 3.4*(Stop*Aside/4L), where L = length of the fuselage.