Bob no offence meant but you keep asking these simple algebraic equations, wouldn't it be better if your son followed the methods shown many times and tried to grasp it himself? The questions can only get harder for him.
Bob- with an equation, think of it as a pair of scales with the equals sign in the middle. You can do anything you like to one side- providing you also do the same to the other side, so it remains equal.
First, try to get the a's on one side and then subtract whole numbers (or add if negative). 3a means 3 x a, so dividing (both sides) by 3, will give you the value of a.
To be fair, if bob and his son aren't very confident with maths then they are probably just making sure they are doing it correctly. I think it's nice that bob is helping his son, would expect that there are loads of kids who don't get the same level of support and interest.
I commend that too sherrardk but Bob has implied he didn't know how to get the answer as 7 but has asked this type of question a lot which suggests they haven't actually understood the method to follow.
I agree sherrardk that it's good to see parents interested. I think though that bob has asked a few questions over the last week which all seem to require pretty much the same approach to solve them so maybe the approach of asking for answers on here hasn't really helped his son. I provided some links on how to solve these too but I'm not sure they have helped yet