Which is the best first step when solving the following system of equations? y is equal to 7 x plus 3 y is equal to 9 x

The first equation gives y = 7x + 3, so you can substitute that expression for y in the second equation, y = 9x. This produces 7x + 3 = 9x. Choice A says to substitute 7x for y, but it leaves out the +3; however, the intended substitution should be 7x + 3. None of the choices states the correct substitution exactly.

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