Z varies jointly with x and y. when x=2 and y=3, z=60. what is the value of z when x=4 and y=9?

A. 360

B. 60

C. 90

D. 40,

Z $ xy then Z = Kxy. When x = 2 and y = 3, and Z = 60, our constant of variation becomes 60 = K * 2 * 3 K = 10. Our constant of proportionality equals 10. We would need that in the second part of the equation. When x = 4 and y = 9, we have Z = 10 * 4 * 9 = 360