A toy and a tent

You will write functions for the surface area of two combined solids, a toy and a tent. Then you will find how tall the cone of the toy must be for the toy to have a given surface area.

The idea. Only the faces that stay on the outside count. A toy with a cone on a hemisphere has area $\pi r l + 2\pi r^2$. A tent has area $2\pi r h + \pi r l$.

Your tasks.

1. In toy_area, return the surface area of a cone of height cone_height on a hemisphere of radius r.
2. In tent_canvas, return the canvas for a cylinder part of height wall and a cone of slant height slant, both of radius r.
3. In cone_height_for, return the cone height that gives the toy a surface area target. Use the formula for the slant height and solve it.
4. Set cost to the cost of the tent canvas of the call tent_canvas(3.5, 3, 3.7) at 90 per square unit, rounded to the nearest whole number.