Chapter 1 - Section 1.4 - Properties of Real Numbers and Algebraic Expressions - Exercise Set - Page 39: 67

$112-x$

You are told that the sum of two numbers (which we will call $x$ and $y$) is 112. Therefore, $x+y=112$. To isolate $y$ and determine its value in terms of $x$, you need to subtract $x$ from both sides. ($x+y$)$-x=112-x$ Therefore, $y=112-x$.