I am trying to do the first part of #12. The answer is -19.

I'm trying things like:

∂f/∂s = ∂F/∂u = ∂F/∂x * ∂x/∂u + ∂F/∂y * ∂y/∂u

but then I am stuck.

Could someone please show me how to do this properly?

Any help would be greatly appreciated!

Thanks in advance!