jmc

The store's revenue is given by: number of books sold $\times$ price of each book, or $p(130-5p)=130p-5p^2$. We want to maximize this expression by completing the square. We can factor out a $-5$ to get $-5(p^2-26p)$.

To complete the square, we add $(26/2{)}^2=169$ inside the parenthesis and subtract $-5\cdot 169=-845$ outside. We are left with the expression $$-5(p^2-26p+169)+845=-5(p-13{)}^2+845.$$Note that the $-5(p-13{)}^2$ term will always be nonpositive since the perfect square is always nonnegative. Thus, the revenue is maximized when $-5(p-13{)}^2$ equals 0, which is when $p=13$. Thus, the store should charge $\boxed{13}$ dollars for the book.