When the mechanic at a car dealership checked the cars on the lot, he found that some were ½ full of gas and some were ¼ full. There were a total of 85 cars and 30 tanks of gas in all. All of the ca

When the mechanic at a car dealership checked the cars on the lot, he found that some were ½ full of gas and some were ¼ full. There were a total of 85 cars and 30 tanks of gas in all. All of the cars have the same size gas tank. How many cars were ½ full?