wx = y...i)

Multiply both sides by x, we get
wx^2 = xy , but wx^2 = 16 (already given)....A), therefore xy = 16.

On the other hand B) i.e. y = 4 tells us that wx = 4, but doesn't tell us the value of xy.

Therefore A) is the correct answer.

The long drawn method would be to susbtitute (1-x) for all values of x in each of the given equations and to see if we get the original equation f(x), as has already been shown by Anurag@Gurome. However, to save time on expanding each equation in its multiples, one can just allocate a value for x. L...