Question

The cost, c(x) in dollars in per hour of running a certain fishing boat is modeled by the function c(x)= 0.9x^2 - 18.1x + 135.1, where x is the speed in km/hour/ At what approximate speed should the boat travel to achieve minimum cost?
Steve
clearly the minimum cost is at the vertex of the parabola, which is at x = -b/2a = 18.1/1.8