Ican be transformed into the equivalent equation of x=6

Ascatterplot is produced to compare the size of a school building to the number of students at that school who play an instrument. there are 12 data points, each representing a different school. the points are widely dispersed on the scatterplot without a pattern of grouping. which statement could be true

Can you me find the missing length. i attached an image.

Which is f(5) for the function –2x2 + 2x - 3?