OG详解-OG4 数学1 Q14

The correct answer is 80. Subtracting the second equation in the given system from the first equation yields (24x + y)-(6x + y)= 48-72, which is equivalent to 24x-6x+y-y =-24, or 18x =-24. Dividing each side of this equation by 3 yields 6x =-8. Substituting -8 for 6x in the second equation yields -8 + y = 72. Adding 8 to both sides of this equation yields y = 80.Alternate approach: Multiplying each side of the second equation in the given system by 4 yields 24x + 4y = 288. Subtracting the first equation in the given system from this equation yields (24x + 4y)-(24x + y)= 288-48, which is equivalent to 24x -24x + 4y - y = 240, or 3y = 240. Dividing each side of this equation by 3 yields y = 80. Dividing each side of this equation by 3 yields y =80.