Let a be the amount needed of 70% pure antifreeze, and let b be the amount needed of 95% pure antifreeze. 0.7a + 0.95b = 180 * 0.9 .........(1) a + b = 180 .............................(2) b = 180 - a ..............................(3) Plugging the expression for b in equation (3) into equation (1), we get: 0.7a + 0.95(180 - a) = 162 ......(4) Solving equation (4) gives the value a = 36, and plugging this value for a into equation (2) we get b = 144. Amounts needed are therefore 36 gallons of 70% pure antifreeze and 144 gallons of 95% pure antifreeze.