Semi-circular yieldable steel arches with a nominal radius of 2 m are used in main entries to a coal mine developed from outcrop under plateau overburden. Seam depth at a point of interest is 716 m where ground pressure on the supports is estimated to be 138 kPa. Determine cross-sectional area (square inches) of A36 steel (250 MPa yield stress) needed and a reasonable set spacing for an appropriate steel safety factor.