Question 879909
You need to correct your equations.
They don't have an equal sign in them. 
I'm assuming it's,
{{{-3x+7y=-5}}}
{{{-15x+35y=-25}}}
So the second equation is 7 times the first equation, so they are the same equation and have an infinite number of solutions.
So then,
{{{-3x+7y=-5}}}
{{{7y=3x-5}}}
{{{y=(3/7)x-5/7)}}}
So then,
({{{x}}},{{{(3/7)x-5/7}}})