A hypothetical metal alloy has a grain diameter of 1.7 ( 10-2 mm. After a heat treatment at 450(C for 250 min the grain diameter has increased to 4.5 ( 10-2 mm. Compute the time required for a specimen of this same material (i.e., d0 = 1.7 ( 10-2 mm) to achieve a grain diameter of 8.7 (10-2 mm while being heated at 450(C. Assume the n grain diameter exponent has a value of 2.1?