A polystyrene component must not fail when a tensile stress

A polystyrene component must not fail when a tensile stress of 1.25MPa (180psi) is applied. Determine the maximum allowable surface crack length if the surface energy of polystyrene is 0.50 J/m2 (2.86 ( 10-3 in.-lbf/in.2). Assume a modulus of elasticity of 3.0GPa (0.435 ( 106psi).