Finding Boxes of Cookies Sold

Elena and Marcus are working on a fundraising project for their school. Elena is selling boxes of cookies, each for $3, while Marcus is selling bags of candies for $2 each.

Together, they want to raise a total of $60. If they sell a total of 30 boxes of cookies and bags of candies combined, how many boxes of cookies, $x$, did Elena sell?

Write your answer as a whole number in the grid.