Given that x+y=4 and x^2-y^2=48.Find the value of 2x-2y

哈哈,又一道题.我再来一次.
先翻译一下这道题：
假如：x+y=4,x^2-y^2=48.试计算2x-2y.
答：
x^2 -y^2
= (x+y)*(x-y)
将x+y=4,x^2-y^2=48分别带入,
48 =4（x-y)
x-y =12
所以,
2x -2y = 2(x-y) =2*12 =24.