SAT Question d1b66ae6: Systems of Linear Equations answer and explanation with Desmos solution

One method for solving the system of equations for $y$ is to add corresponding sides of the two equations. Adding the left-hand sides gives $(-x+y)+(x+3y)$, or $4y$. Adding the right-hand sides yields $-3.5+9.5=6$. It follows that $4y=6$. Finally, dividing both sides of $4y=6$ by $4$ yields $y=\frac{6}{4}$, or $\frac{3}{2}$. Note that 3/2, 1.5, and 1.50 are examples of ways to enter a correct answer.