Two friends are planning on exercise program in order to keep fit. They calculated that, they spent almost 90 minutes per day on exercise. Some of the time will be spent on aerobics.

They prefer to do more aerobics but they could not manage to do more that 60 minutes of aerobics. They discovered that, aerobics use 8 calories per minutes and flexibility exercise use 3 calories per minutes.

How should they use their time to loose the maximum number of calories? Please show your steps of solving how you reach to the answer. Thank you