Best Publishing Company Ever pays its authors really well. For the first 10,000 copies of a book sold, it pays the author $1 per book royalty on the sales. For every copy over 10,000 but less than 50,000, it pays
$1.25 royalty. Once a book sells 50,000 copies sold, they pay $2 royalty. Write a function f(x) that relates
the royalties paid to the number of copies of a book sold?