MATH HELP PLZ!!!
A sparkling-water distributor wants to make up 200 gal of sparkling water to sell for $5.00 per gallon. She wishes to mix three grades of water selling for $8.00, $3.00, and $4.50 per gallon, respectively. She must use twice as much of the $4.50 water as the $3.00 water. How many gallons of each should she use?