Question 861558
{{{X+Y=1}}}
{{{3X+5Y=12}}}
From eq. 1,
{{{X=1-Y}}}
Substitute into eq. 2,
{{{3(1-Y)+5Y=12}}}
{{{3-3Y+5Y=12}}}
{{{2Y=9}}}
{{{Y=9/2}}}
Then,
{{{X=1-9/2}}}
{{{X=2/2-9/2}}}
{{{X=-7/2}}}