5. A sandstone at a depth of 10,000 ft has a Poison's ratio of 0.25 and a poro-elastic constant of 0.72. The average density of the overburden formation is 165 lb-ft}. The pore pressure gradient in the sandstone is 0.38 psi/ft. Calculate the following: a. overburden pressure b. pore pressure c. effective vertical stress d. effective horizontal stress