8. [1.5 pts] We want to design a plastic bottle. It will have inner diameter d1 and outer diameter d2 so that the thickness becomes t=(d2-d1)/2. The inner diameter is determined as 10 cm. The torsional force T from the user's hands is 100 N.m, the shear modulus G=1.575 GPa, and the length of the bottle L = 20 cm. What is the angle of twist (in degree) if: A. The thickness is 1 mm? B. The thickness is 2 mm? Hint: use the J for hollow cross sections.