Answer
The range of forces is $100 \;N\leq F \leq 150\;N$.
Work Step by Step
The force in each case is the pressure multiplied by the area of the plunger.
$$F_i=P_iA=(2.10\times10^5\;N/m^2)\pi(0.0125\;m)^2=1.0\times10^2\;N$$
$$F_f=P_fA=(3.10\times10^5\;N/m^2)\pi(0.0125\;m)^2=1.5\times10^2\;N$$