So you need to do substitution. First solve the easier equation for 1 variable.
x+y=-1 now subtract x to get y=-x-1. Then plug this into the top equation to get 2x+7(-x-1)=2. Next distribute to get 2x+-7x-7=2. Now combine like terms to get -5x=9 so x=-5/9. Now you have to plug this back into the original equation to get y. 2(-5/9)+7y=2, so -10/9 +7y=2. No move terms around to get 7y=28/9 then divide by 7 to get y= 4/9
