Since a frustum is a portion of a solid, three-dimensional figure, and a rectangle is a plane, two-dimensional figure, there can be no such thing as the frustum of a rectangle.

i have an answer for both a frustum of a pyramid and a frustum of a cone

which do you need

frustum of a cone

just give both of them

Most likely, a frustum of a sphere.

Most likely, a frustum of a sphere.

Most likely, a frustum of a sphere.

Most likely, a frustum of a sphere.

There is no frustum of a cone. There is a frustum, which is a cone with the top cut off parallel to the ground.

A frustum. Specifically, a frustum of a triangular pyramid -- as one could also have a frustum of a cone, square pyramid, etc.