Question

x+y=21
2x+4y=54
(Deixem a conta pfv)

Answer 1

x + y = 21 * (-2)

2x + 4y = 54
___________

- 2x - 2y = - 42

2x + 4y = 54


2y = 12

y = 12 / 2

y = 6



X = 21 - y

x = 21 - 6

x = 15




S = { 15 , 6 }