3x + 5y = 10....multiply by 5
5x + 7y = 10 ...multiply by -3
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15x + 25y = 50 (result of multiplying by 5)
-15x - 21y = -30 (result of multiplying by -3)
-----------------add
4y = 20
y = 20/4
y = 5
3x + 5y = 10
3x + 5(5) = 10
3x + 25 = 10
3x = 10 - 25
3x = -15
x = -15/3
x = -5
solution is (-5,5)
