.
(1)     = 12 
(2)     = 4x-16
(1)     = 12
From (2), substitute and replace (y2 - 8y) by 4x-16. You will 
       = 12.
Simplify
      = 12,
      = 0.
Factor left side and get
     (x+11)*(x-1) = 0.
The roots are x = -11 and x = 1.
From this point, complete the assignment on your own.
Solved.
For similar prototypes/samples see the lesson
    - Solving the system of algebraic equations of degree 2 
in this site.
Also, you have this free of charge online textbook in ALGEBRA-I in this site
    - ALGEBRA-I - YOUR ONLINE TEXTBOOK.
The referred lesson is the part of this online textbook under the topic 
"Systems of equations that are not linear".