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

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