Answer: Hello there!
Jack had 3 bags whit b golf balls in each bag, so he originally had an amount of three times b golf balls or 3*b in total.
Now his friend gave him 6 more golf balls, so you need to add 6 to the previous value:
Now Jack has 3b + 6 golf balls in total.
So this equation gives the actual number of balls that Jack has in function of the number b.