Question 131506
You need either a calculator or some paper and pencil for this one. If you have a calc plug the equation into the y= and use 2nd trace maximum.

If you don't have a calculator then you first need to find the zeros. This is easy using factoring.

19x-x^2

Factor out an x x(19-x) set each to zero.
x = 0 and x = 19.

those are where the parabola crosses the x-axis. Since parabolas are symmetrical, the x value of the max falls 1/2 way between the zeros at 9.5

Plug in 9.5 for x in the original equation. Solve for the number of Mosquitos and there is your answer.