An indicator diagram, taken from petrol engine during a test, was divided into 8 strips of equal width. The mid ordinates of the strips measured 17.5, 20.0, 18.75, 12.5, 10.0, 7.5, 5.0,

and 3.75. The scale of the spring used was 60 kPa/mm. Determine the mean effective pressure

of this engine. If the engine cylinder is 80 mm in diameter and 120 mm in stroke, calculate the

net work of the engine per stroke.