Okay so 6.25 a student then it goes to 4.50 for 15 more students at 70 students its 358.75 now it drops another 1.75 so it would be 368.75 for 80 students so the equation is 4.48 x 80 = 368.75. enjoy :D
take your compass on a point on your line. then draw a circle. take the 2 points in which the circle hit the line and draw 2 circles larger than half the distance between he 2 points. take the point that they intersect and and connect it to the line and you point M and it is purpendicular. does that make sense?