Chapter R - Section R.2 - Operations on Real Numbers - R.2 Exercises - Page 20: 47

$-\dfrac{7}{8}$

The given expression, $ -\dfrac{3}{4}-\left( \dfrac{1}{2}-\dfrac{3}{8} \right) ,$ simplifies to \begin{array}{l}\require{cancel} -\dfrac{3}{4}-\left( \dfrac{4}{8}-\dfrac{3}{8} \right) \\\\= -\dfrac{3}{4}-\left( \dfrac{4-3}{8} \right) \\\\= -\dfrac{3}{4}-\dfrac{1}{8} \\\\= -\dfrac{6}{8}-\dfrac{1}{8} \\\\= \dfrac{-6-1}{8} \\\\= \dfrac{-7}{8} \\\\= -\dfrac{7}{8} .\end{array}