Question

Z varies jointly with x and y.

Answer 1

First, let's find "k" the constant of variation:

z= k.x.y (since z varies jointly with x and y)

60 =k.(2).(3) → 60 = 6k and k =10, So z = 10x.y

z= 10(4)(9) = 10(36) and z = 360