Which describes the combined variation in the formula v = ℓwh?

a. v varies jointly with ℓ, w, and h.

b. v varies inversely with ℓ, w, and h.

c. v varies jointly with ℓ and h.

d. v varies directly with w and h

This is the concept of proportionality; we are required to find the combined variation for the volume formula given by:
V=length*width*height
V=lwh
here we see that volume is directly proportional to width, length and height;
therefore the correct answer is:
A] V varies jointly as l,w and h