SAT Question 52cb8ea4: Systems of Linear Equations answer and explanation with Desmos solution

Choice B is correct. Subtracting the second equation, $4x-8y=9$, from the first equation, $7x-5y=4$, results in $(7x-5y)-(4x-8y)=4-9$, or $7x-5y-4x+8y=-5$. Combining like terms on the left-hand side of this equation yields $3x+3y=-5$.