One crew can seal a parking lot in 12 hours and another in 15 hours. how long will it take to seal the parking lot if the two crews work together?

This is a typical work problem in algebra. The approach to this is using the equation: Rt = 1, where R is the rate per person working, t is the amount of time worked by an individual. All their rates must equal to 1. The solution is as follows:

12/x + 15/x = 1

Solving for x,

x = 27 hours

So, if they work together, they can finish the work in 27 hours.