An electric filter purifies air at the rate of 35 liters per minute and uses energy at the rate of 0.8 joules per minute. it also purifies water at the rate of 25 liters per minute and uses energy at the rate of 1.3 joules per minute. the filter is expected to purify more than 1000 liters of air and water while using less than 170 joules of energy. let a denote the number of minutes it spends purifying air and w the number of minutes it spends purifying water.