I need help on this question cause I don’t get it :( please help

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  (x, y) = (3, 9)

Step-by-step explanation:

When you add the two equations together, you get ...

  (y) +(y) = (2x +3) +(-2x +15)

  2y = 18 . . . . . . simplify

  y = 9 . . . . . . . . divide by 2

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When you subtract the second equation from the first, you get ...

  (y) -(y) = (2x +3) -(-2x +15)

  0 = 4x -12 . . . . . simplify

  0 = x -3 . . . . . . . divide by 4

  3 = x . . . . . . . . . add 3

The solution is (x, y) = (3, 9).

Additional comments

These are two equations in two unknowns. There are a number of ways to solve them. One of the simplest is to use one expression for y to substitute for y in the other equation:

  2x +3 = -2x +15

Adding 2x and subtracting 3*, you get

  4x = 12

  x = 3 . . . . same solution as above.

* As with any operation performed on an equation, you must do the same thing to both sides of the equation. For example, "adding 2x" looks like ...

  2x +3 +2x = -2x +15 +2x . . . . . "2x" is added to both sides of the equation

When we collect terms, this simplifies to ...

  4x +3 = 15 . . . . . note that -2x+2x = 0