to find it, evaluate it at the endpoints and the vertex
in form
f(x)=ax²+bx+c
the x value of the vertex is -b/2a
given
c(t)=1t²-10t+76
x value of vertex is -(-10)/1=10
evaluate c(0) and c(13) and c(10)
c(0)=76
c(13)=115
c(10)=76
it reached minimum in 2000 and 2010
porbably teacher wants 2010
the min value is $76
