Mark is 6 years older than his brother Sam. Now, we are asked to represent Sam’s age by a. This means that if Sam is a years old, Mark is (a + 6) years old.
The sum of their ages is 30, this means that when we add their ages together, we get the sum of thirty.
Mathematically this means a + a + 6 = 30
2a + 6 = 30
This is the equation needed to get a. To get a , we proceed to solve the equation to completion.
