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Algebra / Systems of two linear equations in two variables Difficulty: Hard

y = 4 x + 1
4 y = 15 x - 8

The solution to the given system of equations is x,y. What is the value of x-y?

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Explanation

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 44x+1=15x-8. Applying the distributive property on the left-hand side of this equation yields 16x+4=15x-8. Subtracting 15 x 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 .