There are several ways to solve a system of linear equations. We'll take advantage of the second equation since it has the x with coefficient 1 and solve it for x:
Answer is D) 2/3 because you divide the whole equation by 3 scene as 2cups=3gal. In order to get one gal, you need to divide the right side by 3 to make one and what you do to one side of an equation, you must do to the other.