Question 369668
1.{{{x+y=20}}} 
2.{{{x-y=28}}}
From eq. 1,
{{{x=20-y}}}
Substitute into eq. 2,
{{{(20-y)-y=28}}}
{{{20-2y=28}}}
{{{-2y=8}}}
{{{highlight(y=-4)}}}
Then from eq. 1,
{{{x-4=20}}}
{{{highlight(x=24)}}}