Serina wants to solve the following system of equations in the most efficient way. 2 x plus 3 y is equal to 18 x plus 7 y is equal to 31 She plans to solve for x in the first equation as her first step since both 2 and 3 can be divided into 18 Why is Serina mistaken?

To solve for x in the first equation, Serina would divide by 2, leaving x = (18 − 3y)/2, which introduces fractions. In the second equation, x has a coefficient of 1, so it can be isolated directly: x = 31 − 7y. Therefore, solving for x in the second equation is more efficient; that is choice C.

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