Mrs. Kessler bought six books and four CD's. If each CD cost $10, how much did Mrs. Kessler pay for the CD's?

I am unsure why you mentioned the books, but I will attempt to answer this question.

$40

If there are 10 CDs in each book.

$600

mx+89b(-98)nb

step-by-step explanation:

answer: 204

step-by-step explanation:

we are told that the revenue is

x⋅(4080−10x)=−10x^2+4080x

this is a quadratic function, so to maximize it we should find the x-value of its vertex. recall that the x-value of the vertex of the parabola ax^2+bx+c is given by the formula −b/2a.

so in this case, we have a=−10 and b=4080, so the x-value of the vertex is

−b/2a= −(4080)/2(−10)=204