Chapter 2 - Solving Equations - 2-3 Solving Multi-Step Equations - Practice and Problem-Solving Exercises - Page 98: 18

$a=13$

We start with the given equation: $-23=-2a-10+a$ We add $10$ to both sides of the equation: $-23+10=-2a+a$ Now, we combine like terms on both sides of the equation: $-13=-a$ Finally, we divide by $-1$ on both sides of the equation: $a=\frac{-13}{-1}=13$