How do you calculate the weight of rectangular by height?

Answer 1

You cannot.

First, rectangular is an adjective and there is no associated noun so the question does not specify whether it is about a rectangular pyramid, a rectangular bipyramid, a rectangular prism or some other rectangular figure.

Second, in order to find the weight of an object, you need the volume of the shape, the density of its material and the local force of gravity. The volume of the shape requires length and width as well as the height so the available information is hopelessly inadequate.