Answer
$$\approx 1.89\times 10^{9}N$$
Work Step by Step
$$\partial F=P\times \partial A=\rho gh\times \left( W\times \partial h\right) \Rightarrow F=\int ^{D}_{0}\rho gWh\partial h=\dfrac {\rho gWD^{2}}{2}=\dfrac {10^{3}\times 9.8\times 314\times \left( 35\right) ^{2}}{2}\approx 1.89\times 10^{9}N$$