Question 750924
Min occurs at n = -b/(2a) = -(-26)/(2*2.6) = 5


So min occurs at n = 5, plug it in to get the min cost


C(n) = 2.6n^2-26n+640


C(5) = 2.6(5)^2-26(5)+640


C(5) = 575


The min cost is $575