if wx=y, what is the value of xy?
1) wx^2 = 16
2) y = 4
When you see this type of questions, you have to be aware that most of the time you will not be able to solve x, y individually. So try to see if you can form the term (xy) grouped together with the given conditions.
For example, if i tell you 5xy = 10, can you solve for xy? That's the basic idea.
Back to the problem.
1) How can you form (xy) from wx=y and wx^2 = 16. Well, you see can get rid of w by dividing the two equations. Why not just try that. You'll get wx/(w x^2) = y/16. Then 1/x = y/16. Remember you're trying to form the grouped term (xy). So move the 2 variables to the same side and see what you get. 1/(xy) = 1/16.Hence xy = 16.
2) y = 4. Assume x = 2 or x =1, you'll get different answers.