OG详解-OG2 数学2 Q21

The correct answer is  35. The first equation in the given system of equations defines y  as 4x +1. Substituting 4x +1 for y  in the second equation in the given system of equations yields 4(4x +1)= 15x -8. Applying the distributive property  on the left-hand side of this equation yields 16x + 4 = 15x -8. Subtracting 15x from each side of this equation yields x + 4=-8. Subtracting 4 from each side  of this equation yields x =-12. Substituting -12 for x  in the first equation of the given system of equations yields y = 4 (-12)+1, or y =-47. Substituting -12 for x  and -47 for y  into the expression x -y yields -12- (-47), or 35.