A is a variable, meaning that it stands for a number we do not know the value of. Let's imagine we do know the value, let's say it is 2. The expression 20 + 2 = 22. As a increases, so does the answer or value. 20 + 3 = 23, 20 + 16 = 36, 20 + 72 = 92, and so on. Hope this helps!
