A piston, A, has a diameter of .87 cm. A second piston, B, has a diameter of 5.6 cm. Determine the Force "F" necessary to support the 850 N weight in the absence of friction.
Force/Area = constant = fluid pressure
That means Force/(Diameter)^2 = constant
You need to provide information on which piston supports the 850 N weight. If it is the larger piston,
F/(0.87)^2 = 850/(5.6)^2
F = 850*(0.87/5.6)^2 = 20.5 N