The manufacturer of a product that is subjected to repetitive cycles has specified that the product should be removed from service when any crack reaches 15% of the critical crack length required to cause fracture. Consider a crack that is initially 0.02 mm long in a material with a fracture toughness of . The product is continuously cycled between compressive and tensile stresses of 300 MPa at a constant frequency. Assume external cracks for which f = 1.12. The materials constants for these units are n = 3.4 and C = 2 * 10-11. (a) What is the critical crack length required to cause fracture