Answer:
I would say soild 2 because is has the most even ammount of the 4.
I need the sign between the (2/5)x and the 9
(x +4) * (x -1)
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Try the suggested solution with short explanation; red line means the curve between the first point (on the midline) and the closest maximum; the - - - - line means the curve between the first point (on the midline) and the closest minimum.