After What Length of Time Does Tc-99m (Obtained from Mo-99)

After what length of time does Tc-99m (obtained from Mo-99) reach the maximum of its activity in a generator? The half-life of Tc-99m is 6.02 h, and that of Mo-99 is 66.7 h.

A) 3.96 × 10^-4 d
B) 3.96 × 10^-2 d
C) 19.1 d
D) 22.9 d