Experimentally, it has been observed for single crystals of a

Experimentally, it has been observed for single crystals of a number of metals that the critical resolved shear stress tcrss is a function of the dislocation density ?D as

where t0 and A are constants. For copper, the critical resolved shear stress is 2.10MPa (305psi) at a dislocation density of 105 mm-2. If it is known that the value of A for copper is 6.35 x 10-3MPa-mm (0.92psi-mm), compute the tcrss at a dislocation density of 107 mm-2.