Multiply the first equation in y + 3x = -1 and 2y - 5x =31 by -2, to obtain:
-2(y + 3x = -1) => -2y - 6x = +4
2y = 5x + 31 (this is the 2nd equation)
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-6x = 5x + 35, or -11x = 35, or x = -35/11
Subst. -35/11 for x in either of the given equations, to find the value of y.
Then write y our solution in the form (-35/11, ? ).
As always, you should check your answer.