Ok here is the answer I wrote it out for you
Overestimate because then the gardener could possibly save the left overs in case they get a chance to use it or they could give it to someone who may need it.
The value of it is numbers
So she makes 80,000p every month on average?
For
y=ax²+bx+c
the x value of the axis of symmetry is -b/(2a)
so test them
A., -b/(2a)=-(-8)/(2*-2)=8/-4=-2, yep
B. -b/(2a)=-2/(2*1/2)=-2/1=-2, yep
C. -b/(2a)=-(-16)/(2*4)=16/8=2, nope, need -2
D. -b/(2a)=-12/(2*3)=-12/6=-2, yep
answer is C