How do I combine these? It's a question I need to answer today in math class but I do not get it
You can think of x as the number of things (say apples):
If I have 4 apples and 5 apples, how many apples do I have? (9 apples)
Likewise, you have 4x and 5x, so you have 9x altogether.
similarly, if I have 9 apples and you take away 4 apples from me, how many apples do I have? (5)
likewise 9x - 4x = 5x.
Let's look at 2 items now.
If I have 4 apples and 5 oranges, there is no way you can add them up different they are different items.
So 4x + 5y = 4x + 5y.
Hope this help you have a better understanding of algebra.