Answer:
z = 4xy
Explanation:
IF Z varies directly with the product of x and y, then;
Z = kxy
k is the proportionality constant
If x=2,y=0.5, z=4,
4 = k(2)(0.5)
4 = k * 2 * 1/2
4 = k
Swap
k = 4
Substitute into the original expression
z = kxy
z = 4xy
This gives the required expression