If star is a binary operation on a subset of the real numbers, for which of the following definitions is star commutative?

W) \(a\) star \(b=a-b\)

X) \(a\) star \(b=a/b\)

Y) \(a\) star \(b=\) the fraction with numerator \(a+b\) and denominator \(a\) times \(b\)

Z) \(a\) star \(b=a^{2}-b^{2}\)
Y) \(a\) star \(b=\) THE FRACTION WITH NUMERATOR \(a+b\) AND DENOMINATOR \(a\) TIMES \(b\)