OG详解-OG8 数学2 Q11

Choice C is correct. The given system of linear equations can be solved by the substitution method. Substituting -3x for y from the first equation in the given system into the second equation yields 4x +(-3x)= 15, or x = 15.
Choice A is incorrect and may result from conceptual or calculation errors. Choice B is incorrect and may result from conceptual or calculation errors. Choice D is incorrect. This is the absolute value of y, not the value of x.