Combine “like” (same type) terms. You see three terms and and equals sign.
Two terms on the left side and one term on the right side (of the equals sign).
One term is a number and two terms have the variable x (with an implied exponent of 1).
If you had two numbers, you could combine them because they are “like” terms.
In this case, you have two like terms with x. So you can combine them.