How many gallons of gasoline will it take to mow one lawn if you maintain the rate of 1/2 gallon of gasoline per 1/4 lawn mowed? plz

It will take 4 gallons of gasoline to mow the lawn. Since .5 of the gasoline mows .25 of the lawn you are going to multiply the amount of gasoline by 4, since it is increasing by a rate of .5 to .25. 
1/2 gallon = 1/4 lawn
1 gallon = 2/4 lawn
1 1/2 gallons = 3/4 lawn 
2 gallons= 4/4 lawn