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

12345678-112345678910-1-2Day of Week[Graphs generated by this script: initPicture(-1,8,-2,10);axes(1,1,1,1,1);marker="dot";line([1,9],[2,4]);line([2,4],[3,3]);line([3,3],[4,6]);line([4,6],[5,7]);line([5,7],[6,1]);line([6,1],[7,8]);text([4,-1],"Day of Week","below");]

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