Which is the best first step and explanation for solving this system of equations?
(3x + y) – (x + y) = 7 – 3
Subtract equal quantities from both sides of the first equation.
(3x + y) + 3 = 7 + 3
Add the same number to both sides of the first equation.
(3x + y) + (x + y) = 7 + 3
Add equal quantities to both sides of the first equation.
(3x – x) – (y + y) = 7 – 3
Subtract the second equation from the first equation.