A test specimen is subjected to a longitudinal tensile stress of 200 MPa and a transverse compressive stress of 50 MPa. 

a) Write down the stress matrix and draw Mohr's circle. 

b) Determine the stress matrix for maximum shear using Mohr's circle and describe the directions of maximum shear. 

c) Determine the normal stresses using Mohr's circle when the specimen is oriented at a counter-clockwise angle of 15°.