what number should be added to -7/12 to get 1/24

Suppose the required number to be added is x.
So we have;
$$\begin{gathered} x+\left(\frac{-7}{12}\right) = \frac{1}{24} \\ \Rightarrow x-\frac{7}{12} = \frac{1}{24} \\ \Rightarrow x = \frac{1}{24}+\frac{7}{12} \\ \Rightarrow x = \frac{1+14}{24} = \frac{15}{24} = \frac{5}{8} \end{gathered}$$
Therefore required number to be added is $\frac{5}{8}$.