Question 305182
First you would need to find how many square feet are in the lawn.  
30*60=1800

Next, you know that there are four quarts in a gallon, and you need 3 quarts per square foot, so that means you need 3/4 of a gallon of water per square foot.  
3 quarts 
--------- = 3/4
4 quarts        

Then, you would multiply the number of gallons you need per square foot by the number of square feet in the lawn.
3/4*1800=1350


1350 gallons of water will be needed to water a 30 by 60 ft lawn, watering 3 quarts of water per square foot.