Draw line segment of 7.5cm.take compass of length 6cm on one side of the line segment and make at another side of the linesegment with 7cm of radius of compass cut the arc of 6cm.join these points.a triangle is formed. Now on the line segment 7.5cm take compass of more than half of the line segment length i.e.more than 4 and draw arcs above and below the line segment. Now at another end of the line segment with the same length of the compass cut the arcs drawn before above and below the line segment. Now take a scale and join the two points where those arcs were cut above and below. That is the perpendicular verify the distance of the perpendicular bisector is 3.75 from the point of linesegment