The correct answer is Choice A.
Graph the linear equation on the $xy$-plane and identify the right triangle.
Choice B is incorrect and may result from finding the area of a rectangle.
Choice C is incorrect and may result from using the constant 18 in the equation.
Choice D is incorrect and may result from using the coefficients as the legs of the right triangle.
✨ Expert's Tip ✨
If the two lines are parallel and have the same $y$-intercepts, there will be infinite number of solutions to the system.