Answer:
Option A.
Explanation:
We are asked to add these 2 expressions.
First, we should know how to combine like terms.
What is combining like terms?
Combining like terms is adding 2 or more numbers, or variables that are alike.

Let's first begin by combining s and t. We can combine like terms for these two variables.


-3 doesn't have any like terms, meaning it'll stay as -3.

Therefore, our answers matches with Option A.