Brian spent 60% of a weeks time working on drawings for a new apartment building. If Brian spent 18 hours working on projects other than the apartment building, compute the total hours worked

This means that he spent 40% of his time working on other projects. We also know that he also spent 18 hours.

Let's say he spent t hours working on everything. So. 4t=18

t = 45

Total hours worked is 45. He spent 27 hours on the apartment building.