A circular disc mounted on a shaft carries three masses of 4 kg, 3 kg, and 2.5 kg at a radial distance of 75 mm, 85 mm, and 50 mm, respectively. The angular positions of the masses are measured counter-clockwise from the reference line along the x-axis and is given as 45°, 135º, and 240°, respectively. Using the "Graphical method” of force balance, determine the amount of the mass of counterbalance required at a radial distance of 75mm.