$(24)3.$ Triaxial compressive strength test was done on a rock specimen and failure angle of the sample was found as $69.$ Uniaxial compressive strength of this rock was found as $50$ MPa $.$ According to these data, answer following questions:

a$)$ Find "Internal frictional angle $()"$

b$)$ Find "Cohesion $($c$)"$ value.

c$)$ If ${}_3=10$MPa, determine ${}_1$ value from the graph.

d$)$ Check the stability of specimen under following load conditions

$($prove that specimen would fail or stay stable$)$