If f(x) = -x2+9x-18, then what is the maximum value of f(x)?

F(x)=-x^2+9x-18
=-(x^2-9x+18)
=-((x-3)(x-6))
As leading coefficient is negative, between the two zeros is the maximum
=(3+6)/2
=(9)/2
x=4.5
=-(4.5)^2+9(4.5)-18
=2.25

Letter c so sorry if i’m wrong ):

This does not make sense