Part B

In this part, you will write a function that computes the shipping cost, given the weight of the package.

If $0$ weight $1\mathrm{.}0,$ return $$3\mathrm{.}50$

If $1\mathrm{.}0$ weight $3\mathrm{.}0,$ return $$5\mathrm{.}50$

If $3\mathrm{.}0$ weight $10\mathrm{.}0,$ return $$8\mathrm{.}50$

If $10\mathrm{.}0$ weight $20\mathrm{.}0,$ return $$10\mathrm{.}50$

If $10\mathrm{.}0$ weight $20\mathrm{.}0,$ return $$10\mathrm{.}50$

If weight is invalid, return $-1.$