Answer:
(c) 4x + 2y = 14; x + y = 3
Explanation:
The given equation will be the result of eliminating the y-variable from the system. When we do that for the different answer choices, we get ...
a
Add the two equations: (3x -y) +(x +y) = (15) +(7) ⇒ 4x = 22
b
Add the two equations: (x +3y) +(-x -3y) = (24) +(16) ⇒ 0 = 40
c
Subtract twice the second from the first.
(4x +2y) -2(x +y) = (14) -2(3) ⇒ 2x = 8 . . . . the system we're looking for
d
Add the two equations: (2x +2y) +(-2x -2y) = (8) +(8) ⇒ 0 = 16
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Additional comment
When the equation reduces to 0 = constant, and "constant" is not zero, it means the system of equations has no solution. (The equations describe parallel lines.)