Answer: x = -5 and y = 10
Explanation:
the first thing you must always remember is that you can't solve a two-variable equation without creating a system, which i assume you've already learned.
the first thing you want to do is set up your system using the bracket { and writing x+y = 5 at the top and 2x+y = 0 at the bottom. (the 0 isn't specified in your picture but when it's not there, we assume it's equal to 0 at the moment.)
now that you've done this, look at your system. we can see that isolating both x and y are possible. I decided to isolate the x so that we could multiply the substitution by 2 in the second part of the system and get over it.
so your first step is changing the top of the system and rewriting it as x=5-y (moving the y to the right side will change it's value, making it negative)
because you've now isolated the x you can plug it into the second equation. it should look something like this
x=5-y
2(5-y) + y = 0
got it? good, let's move on. no opening the parenthesis, we multiply the 2*5 and the 2*-y therefore changing our equation once again. it should now be 10-2y+y=0. if you've already simplified the y's, you should have 10-y=0
you're one step away from finding y's value. we move the y to the right side of the equation and voila! y=10
but you're not done just yet. using the y value we can plug it into the top part of our system. to remind you, it was x=5-y
because y=10, we rewrite the equation as x=5-10, therefore making x=-5
hope this helped!