#### Answer

$180-x$

#### Work Step by Step

You are told that the sum of two angle measures (which we will call $x$ and $y$) is 180 degrees.
Therefore, $x+y=180$.
To isolate $y$ and determine its value in terms of $x$, you need to subtract $x$ from both sides.
$(x+y)−x=180−x$
Therefore, $y=180−x$.