Here is the way I solved this.
Let p = part-time employees and f = full-time employees. We know that \(p = \frac{f}{3}\) because they are 25% of the total employees while f is 75%, thus \(\frac{25%}{75%} = \frac{1}{3}\).
Now, to find the part-time hours worked in relation to full-time hours worked, we multiply \(\frac{1}{3}\) by \(\frac{3}{5}\) and get \(\frac{1}{5}\).
Note that the answer is not \(\frac{1}{5}\), because it is asking for the fraction of part-time work out of the total number of work by ALL employees, not the ratio between part-time work and full-time work. Thus, we must add part-time work and full-time work. If part-time work is \(\frac{1}{5}\) of full-time work, that means the total work is \(\frac{1}{5} + \frac{5}{5} = \frac{6}{5}\).
Now we divide part-time work by total work: \(\frac{1}{5} / \frac{6}{5} = \frac{1}{6}\)
This might be an unconventional or inefficient way to solve, so if anyone has a better way please share!