Question

How do I find the value of b

Answer 1

The initial amount is 8. That is b.
The amount it grows is 2x, 2 employees per quarter.

y = 2x + 8

Answer 2

b would be the addition of the starting 8 employees. you gotta add that into equation. you cannot multiply that number thats why it is a plus b = +8, no matter what ax value is there is always the 8 employees who starting first.