Find constants $\displaystyle {A}$ and $\displaystyle {B}$ so that the graph of:

$\displaystyle {f{{\left({x}\right)}}}=\frac{{{A}{x}+{3}}}{{-{19}+{B}{x}}}$ 

will have $\displaystyle {x}={5}$ as a vertical asymptote and $\displaystyle {y}={20}$ as a horizontal asymptote. Express $\displaystyle {A}$ and $\displaystyle {B}$ as fractions of lowest terms. 

 $\displaystyle {A}=$            $\displaystyle {B}=$