solve each system by elimination

Solve the following system:
{7 x + 8 y = 14 | (equation 1)
-7 x - 7 y = -21 | (equation 2)
Add equation 1 to equation 2:
{7 x + 8 y = 14 | (equation 1)
0 x+y = -7 | (equation 2)
Subtract 8 × (equation 2) from equation 1:
{7 x+0 y = 70 | (equation 1)
0 x+y = -7 | (equation 2)
Divide equation 1 by 7:
{x+0 y = 10 | (equation 1)
0 x+y = -7 | (equation 2)
Collect results:
Answer: | x = 10          and           y = -7

Α=7x+8y=14 

B=-7x-7y=-21

 Α+Β=...y=14-21 y=-7 so 

in A=7x+8(-7)=14<=>

<=>x=(14+56)/7<=>x=10 

x=10 and y=-7