To factor -1/8 out you need to find a number that multiply by -1/8 be equal to each term in the expression.
To find those numbers you divide each term into -1/8:
[tex]\begin{gathered} \frac{-\frac{1}{8}y}{-\frac{1}{8}}=y \\ \\ \frac{24}{-\frac{1}{8}}=-24\cdot8=-192 \end{gathered}[/tex]Then, the factors are:
[tex]-\frac{1}{8}y+24=-\frac{1}{8}(y-192)[/tex]