Answer:
Assuming its asking which is the easiest one to use substitution its the last one: y= 2x : x + y = 28
Explanation:
Because y and x are already one opposite sides you can substitute y in the 2nd equation with 2x. So you'll get 3x = 28 so x = 9.333333334. Then you plug your answer for x in the original equation to get y = 18.666666667