Finding x + y from Linear Equations

Maria and John are both solving a problem involving the same two linear equations:

1. $2x + 3y = 12$

2. $4x - 6y = 24$

They are asked to find the value of $x + y$. However, Maria mistakenly thinks she can solve for $y$ in terms of $x$ from the first equation, while John decides to substitute $y$ from the second equation into the first. Determine the correct value of $x + y$ by solving the system of equations.