How do i solve y=x+8, x+y=2 by substitution

The first EQ is already an answer so you need to grab x+8 and plug it into the y of the second EQ because x+8 is equaled to y. after your plug it in it should look like x+x+8=2 add like terms you should get 2x+8=2 then you subtract 8 on both sides. 8 on the left side will cancel out and 2-8= -6 so it looks like 2x= -6 then you divide x by both sides leaving you with x= -3 and if you are looking for y then just plug in and do steps again:)

Yes the slope to this is -5