Combining like terms must always be in descending order.
Start with the exponents.
As we see, there is no other exponents so we would leave it as such.

Progress on to the next greatest which are the variables.
Add all of the coefficients

Lastly, move on to the single numbers.
Add them together as shown above, but this time there are no coefficients so it is just a matter of addition and subtraction

Therefore, the answer is:
