Question: 12 of x is equal to 6 of y?
Answer: If 12% of x is equal to 6% of y, which percentage of y will 18% of x equal to? Your figures indicate that y is twice as large as x, so 18% of x would be 9% of y. If we arbitrarily say x = 100 and y = 200, then 12% of x is 12 which is 6% of y.