Question 1015847
Keep in mind, there are multiple ways to solve this. Mine is just one method I find easy to explain, and repeatable for students. 

Juan can mow .25 lawns per hour.
Pedro can mow 1/3 lawns per hour. 

Together they mow 7/12 lawns per hour so it will take 12/7 hours or 1 hour, 42.86 minutes per whole lawn.