$${\frac{{\mathtt{a}}}{{\mathtt{c}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{b}}}{{\mathtt{d}}}}$$
insert the values for a, b, c and d
$${\mathtt{\,-\,}}{\frac{{\mathtt{7}}}{{\mathtt{82}}}}{\mathtt{\,-\,}}{\frac{{\mathtt{8}}}{{\mathtt{20}}}} = {\mathtt{\,-\,}}{\frac{{\mathtt{199}}}{{\mathtt{410}}}} = -{\mathtt{0.485\: \!365\: \!853\: \!658\: \!536\: \!6}}$$
.$${\frac{{\mathtt{a}}}{{\mathtt{c}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{b}}}{{\mathtt{d}}}}$$
insert the values for a, b, c and d
$${\mathtt{\,-\,}}{\frac{{\mathtt{7}}}{{\mathtt{82}}}}{\mathtt{\,-\,}}{\frac{{\mathtt{8}}}{{\mathtt{20}}}} = {\mathtt{\,-\,}}{\frac{{\mathtt{199}}}{{\mathtt{410}}}} = -{\mathtt{0.485\: \!365\: \!853\: \!658\: \!536\: \!6}}$$