
1) In this problem, the first thing to do is to enlist the categories:
workers time to clean # apartments
8 2h15 12
8 9 x
2) Note that the number of cleaners is the same. So, we can pick the ratios that fall under the category time and #apartments
We need to convert that 2h 15 into decimal form before setting the ratios:

3) Now, we can set the ratios and solve for x:

Thus, the answer is 48