Chapter 9 - Basic Algebra - 9.2 Adding and Subtracting Signed Numbers - 9.2 Exercises - Page 639: 38

$-\frac{7}{8}$

The additive inverse is the opposite of a number. The sum of a number and its additive inverse is 0. Therefore, the additive inverse of $\frac{7}{8}$ is $-(\frac{7}{8})=-\frac{7}{8}$. We can check to make sure the sum of these two numbers is 0. $-\frac{7}{8}+\frac{7}{8}=\frac{7}{8}-\frac{7}{8}=0$