P$2.$ A prestressed square concrete pile with dimensions of $460mm$ and a length of $20m$ is fully embedded in sandy soil. For the sandy spil, we have cohesion C $=18\mathrm{.}6k\frac{N}{m^2}$ and angle of internal friction angle $=30$ degrees. Estimate the tip resistance of the pile using the Vesic method. $($assume $I_r=I_r=75)$