Find the value of x really need !

Solve 2x+y=3 x+y=5 in substitution method

Ineed i been stuck on this question since yesterday

Answer asap and if you do you will get brainliest. catherine buys a gallon of ice cream from the store. after taking it home, she eats a fifth of a gallon of ice cream. her sister eats some of the ice cream as well. if two-thirds of the original amount of ice cream is left, then what fraction of a gallon of ice cream did her sister eat?