What is the equation for the exponential parent function

John bought 5 lemons and used 2 of them for a salad how much did he use for.a salad . he used % of the lemons.

Marquise has 200 meters of fencing to build a rectangular garden. the garden's area (in square meters) as a function of the garden's width w w (in meters) is modeled by: a ( w ) = − w 2 + 1 0 0 w a(w)=−w 2 +100w what side width will produce the maximum garden area? meters

How can i differentiate this equation?