A dilatometer test was conducted in a clay deposit. The groundwater table was located at a depth of 3 m below the surface. At a depth of 8 m below the surface, the contact pressure (P₀) was 280 kN/m² and the expansion stress (p₁) was 350 kN/m². Determine the following:

a. Coefficient of at-rest earth pressure, K_o

b. Overconsolidation ratio, OCR

c. Modulus of elasticity, E_s

Assume σ'_o at a depth of 8 m to be 95 kN/m² and µ_s = 0.35.