Substituting ② into ① is 2x+15-4x =11.

Solution: x=2,

Substitute x=2 into ② to get y = 7.

So;

(2) Transform the original equation into:

Let ②×2: 4x+6y+6=0 ③.

( 1)-(3): y= 1，

Substitute y= 1 into ② to get: x =-3.

So ...