Two tanks, X and Y, are filled to capacity with jet fuel. Tank X holds 600 gallons more than tank Y. If 100 gallons of fuel were to be pumped from each tank, tan X would then contain 3 times as much fuel as thank Y. What is the total number of gallons of fuel in the two full tanks?

Answer: 1,400

I am not a native English speaker. So I cannot really understand the question itself.

I set the equation

y + 600 = x

3y = x

and then x = 900, y = 300.

However, it was wrong.

Can you help me?