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Ralph is 3 times as old as Sara. In 6 years, Ralph will be only twice as old as Sara will be then. Find Ralph's age now.

Which of the following equations could be used to solve the problem?

3x + 2x
x + 6 = 2(3x + 6)
3x + 6 = 2(x + 6)
3x + 6 = 2x + 6