Although you have not included the statements about the solution to the set of the given equations, I can explain you what happen with that system.
You can arrive to the same conclusion by any method of solution of systems that you like.
The quickest in this case, is to multiply the equation of the lIne F by 5.
That leads to: 5 (x + y) = 5(8)
⇒ 5x + 5y = 40.
Now you can realize that the two representations (equations) correspond to the same line.
That means that there are infinite solutions, this is infinity values of x and y meet both equations.
If you graph line E and line F they overlap in the entire domain, so the graphing method also tells you that you cannot find one solution but infinite soluttions.