The roots are 0 and 281, so the middle of the parabola or the aos is 140.5. The vertex will be at (140.5,71)

So,

f(x)=a(x)(x-281)

sub in the vertex and solve for a.

71=a(140.5)(140.5-281)

a= -284/78961

There fore, the function is f(x)= -284/78961 (x)(x-281)