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([1,7],[2,4]);line([2,4],[3,2]);line([3,2],[4,8]);line([4,8],[5,6]);line([5,6],[6,5]);line([6,5],[7,9]);text([4,-1],"Day of Week","below");]

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