Question 829473
1.{{{3x + y = 4}}}
2.{{{2x + y = 5}}}
Subtract eq. 2 from eq. 1 (or form a linear combination of eq. 1 and (-1)*eq. 2), 
{{{3x+y-2x-y=4-5}}}
{{{highlight(x=-1)}}}
Then use either equation to solve for y.
{{{3(-1)+y=4}}}
{{{-3+y=4}}}
{{{highlight(y=7)}}}