This problem is a straightforward example of rearranging and integrating the v-K equation. The only information required to perform this integration are the limits on K and the constants D and n in the equation.As the equation is plotted in the graph provided, the constants are easy to obtain. The upper limit on the integration Kf requires a value of the critical crack size for fracture under the given applied stress. What equation for fracture toughness involves E, R and ac?