Answer:
In ten year you will be 10 years older than you are now and so will your brother. The 6 years difference will remain if no one dies.
Explanation:
You are z years old
Your brother is 6 years younger than z years; z - 6 years
In 10 years time, you will be z + 10 years
Your brother will be z - 6 years + 10 years = z + 4 years
OR
In 10 years time, you will be z + 10 years
You brother is still 6 years younger than you, so is z + 10 years - 6 years = z + 4 years