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Find the difference (8ab+a+2) - (3ab+6)

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

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