$$\left({\frac{\left(-{\mathtt{7}}\right)}{\left({\mathtt{x}}{\mathtt{\,-\,}}{\mathtt{8}}\right)}}\right) = \left({\frac{{\mathtt{a}}}{\left({\mathtt{8}}{\mathtt{\,-\,}}{\mathtt{x}}\right)}}\right)$$ solve for a
$$\\\left( { (-7)\over(x-8) } \right) = \left( { (a)\over(8-x) } \right) }\\\\ \left( { (7)\over(8-x) } \right) = \left( { (a)\over(8-x) } \right) }\\\\ \boxed{7=a}$$
