The line graph below shows the number of times Maria drove her car each day of the week.

[Graphs generated by this script: initPicture(-1,8,-2,10);axes(1,1,1,1,1);marker="dot";line([1,6],[2,4]);line([2,4],[3,9]);line([3,9],[4,8]);line([4,8],[5,1]);line([5,1],[6,3]);line([6,3],[7,7]);text([4,-1],"Day of Week","below");]

How many times did Maria drive her car on day 4?