Question

$x+y=10 \\ x-y=5$

Answer 1

(I) x + y = 10
(II) x - y = 5

(I) x = 10 - y
(II) 10 - y - y = 5
(II) -2y = 5 - 10
(II) y = 5/2

(I) x = 10 - y
(I) x = 10 - 5/2
(I) x = 15/2