Approximately how much exercise should the average 14-year-old girl do daily to maintain her weight?

Wrong question... Daily exercise is extremely important for fitness, good health and weight management. That said, you can eat your way through any amount of exercise. For weight management and if weight is a concern, then eating a proper diet is the bottom line of how you make it happen. If you have a weight problem, even if you're exercising hours a day, you won't succeed on a diet of cookies and french fries.