Answer
$-\frac{3}{4}d$
Work Step by Step
The distributive property holds that $a(b+c)=ab+bc$. Therefore, we can use the distributive property to combine like terms.
$\frac{3}{8}d-\frac{9}{8}d=(\frac{3}{8}-\frac{9}{8})d=(\frac{3-9}{8})d=(-\frac{6}{8})d=-\frac{3}{4}d$
