Scientists are conducting trails on a new disinfectant for use in hospitals and doctors offices. After conducting several trials, they found that it decreases the presence of bacteria by 35% each second that it is applied to a surface. The next trail will apply it on a desk surface with approximately 20,000 cells of bacteria on it. Which logarithmic function model the time, f(n), in seconds, it will take the number of cells to decrease to a value of n?