Suppose z varies directly with y and directly with the cube of x . If z = 8640 when x = 6 and y = 10, what is z when x = 9 and y = 2?

Question

Suppose z varies directly with y and directly with the cube of x . If z = 8640 when x = 6 and y = 10, what is z when x = 9 and y = 2?

Answer 1

z = kyx³

8640 = k(6)(10) So, k = 144.

z = 144yx³

Replace x by 9 and y by 2. Then solve for z.