12.6 The tubular casing of a solid rocket booster (SRB) for the space shuttle has a mean radius of 71.76" and a wall thickness of 0.479". The maximum working pressure

it has to contain is 6.303 MN m-2. What is the hoop stress at this pressure? The casing is made from D6AC steel with a yield strength of 1244 MN m-2. What is the safety factor S for the casing?