If W_u Is the Union Wage and W_n Is the Nonunion

If W_u is the union wage and W_n is the nonunion wage,the pure union wage advantage is:

A) $$\frac { W _ { n } - W _ { u } } { W _ { u } } \times 100$$
B) $$\frac { W _ { n } } { W _ { u } } \times 100$$
C) $$\frac { W _ { u } - W _ { n } } { W _ { n } } \times 100$$
D) $$W _ { n } - W _ { u }$$