Question 187583
{{{x + y = 15}}}
{{{3x-1 = y}}}

{{{x + (3x-1) = 15}}}
{{{4x - 1 = 15}}}
{{{4x = 16}}}
{{{x = 4}}}

{{{3*4 - 1 = y}}}
{{{12 -1 = y}}}
{{{11 = y}}}