A Ni-based superalloy has 0.2 μm thick oxide layer. When placed in a burner rig to test for oxidation, it was observed to grow to 0.3 μm in 1 h. If the superalloy follows a parabolic oxidation law (x2 = a + bt, where x is the thickness, t is the time, and a and b are constants) what is the thickness after one week?