How many times a week should an individual exercise?

That depends on the person and their goals. You can do cardio every day of the week if you really want to, but you should give your body a day or two to rest. Also, you should not do strength training with the same muscle groups on back to back days.

All that being said, be sure to give your body adequate food fuel and avoid overtraining by taking 1 or 2 days off per week.