7. William buys a book for . If he pays with a bill, what will be his
   change ? Write and solve an equation to find out.

To determine the change William will receive, we can set up the equation:

Now, solving for :

So, William will receive as change.

To make math transactions easier, it’s great to round to the nearest whole number when possible! For instance, if you rounded to , you could quickly see that he’d get about . But be careful— rounding can lead to errors if exact change is needed. Always double-check calculations to stay financially fit!