Solve the system by elimination: 4x + 3y = 25 and 2x - 3y = -1. What is the value of x + y?

Add the equations to eliminate $y$: $(4x+3y)+(2x-3y)=25+(-1)$, so $6x=24$ and $x=4$. Substitute into $2x-3y=-1$: $8-3y=-1$, so $y=3$. Check in the first equation: $4(4)+3(3)=25$. Then $x+y=4+3=7$, choice D. Choice B ($4$) is $x$ alone, and the question asks for the sum. Choice A ($1$) is the difference $y-x$ with a sign slip or $x-y$, and choice C ($12$) is the product $xy$. Always reread what the question asks for after solving the system.