Answer:
About 2 of their next 5 deserts sold would be brownies.
Let's represent this by fractions. If 8 out of the 20 desserts they sold were brownies, that would make the fraction 8/20 represent how many brownies were sold.
Now if you reduce this fraction, you get 2/5, which tells about how many brownies will be sold in the next 5 brownies judging by the other data.