$3.$According to the Coulomb's general equations, caculate the active and passive lateral pressures $(K_{ac}$ and $K_{pc}).$

The angle $$ is $20$ degrees. The soil infront of wall is horizontal.

The angle ${}_1$ is $10$ degrees and ${}_2$ is $20$ degrees.

The soil is cohesionless. Assume $($the friction between wall and soil$)$ is $8$ degrees.

Please answer everything correctly with full working out and explanation.