OG详解-OG10 数学1 Q20

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.