Red and Green Marbles

The ratio of red marbles to green marbles in a package is 3 to 5. 25 green marbles are in the package. What is the smallest number of marbles, and of which color, would you have to add to the package of marbles so that the ratio of red marbles to green marbles becomes 5 to 8?

(Source: Adapted from Mathematics Teaching in the Middle School, May 1994)