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

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