Chapter 1 - Introduction to Algebraic Expressions - 1.6 Subtraction of Real Numbers - 1.6 Exercise Set - Page 49: 27

45

The opposite of a real number $a$ is written as $-a$. Therefore, the opposite of $a$ is the negative of $a$. Furthermore, $-(-a)=a$. That is, the opposite of the opposite of $a$ is $a$. Therefore, if $x=-45$, then $-x=-(-45)=45$.