The sum of two rational number is $ \large\frac{-1}{2}$. IF one of them is $\large\frac{-9}{10}$. find the other

Question

$\begin{array}{1 1} \frac{5}{2} \\ \frac{2}{5} \\ \frac{3}{10} \\ \frac{10}{3} \end{array} $