Answer: you are 8 years old.
Explanation:
You are x years old and your brother is 7years old. The sum of your ages is
(x + 7) years
If you take 80% of the sum of our ages the result will be 12. 80% of the sum of your ages is
80/100 × (x + 7) = 0.8(x + 7)
Therefore,the equation would be
0.8(x + 7) = 12
0.8x + 5.6 = 12
0.8x = 12 - 5.6
0.8x = 6.4
x = 6.4/0.8
x = 8 years