The force generated by a spring is given by F = kx....?

where k is the spring constant and x is the deflection of the spring. The spring constant is 8kN/cm. The pressures are 5000kpa 10000 kpa and 1000 kpa. If the piston diameters are 8cm and 3cm how far will the spring be deflected? Answer is 1.72 but how do you obtain that. I got 1.53 on my try.