People say there's a math help thread, but I couldn't find it, so here we go. It's a word problem, and we are learning about variation functions.

"The photograph shows a great white shark caught off Catalina Island. The shark was 15 feet long, and weighed 2000 pounds."

a. Assuming that all great white sharks have similar proportions, how should the weight of a great white shark vary with it's length?

The back of the book says that the weight varies directly with the cube (of it's length). I get why it varies directly, but why does it vary with the cube of the length?
because to relate length to weight, you must relate length to volume. The volume would be an infinite amount of cubes (length * width * height) added together. Since in a cube the l w and h are identical, the length cubed varies directly with weight. Gosh, I'm such a bad explainer. sorry if you don't understand.
Ya, but weight and volume aren't equal (they could be, but most likely not). It will always be K * volume = weight where k is a constant. For example, if the volume is 2 and the weight is 4, the k will always be 2.
Well he has weight and length, they varies depending on the volume. Think you have a fat guy who is 6'4'' tall and a skinny guy who is 6'4'' tall. Who is more heavy? Get the picture?
Yeah, what everyone has been saying. You are relating a 3 dimensional characteristic of the shark (volume, weight) to a 1 dimensional characteristic (length), so the it must be cubed in order to convert.