help me plz i do not understand and plz DO NOT TAKE MY POINTS BECAUSE I WILL REPORT YOU!!! thank you and you can anser or explane what i have to do to get the anser idc but plz dont steel my points

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