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

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