Suppose that z varies jointly with x and y.

Find the constant of proportionality k if z = 1062.4 when y = 16 and x = 8.
k =
Using the k from above write the variation equation in terms of x and y.
z =
Using the k from above find z given that y = 21 and x = 28.
z =

If needed, round answer to 3 decimal places.
Enter DNE for Does Not Exist, oo for Infinity