You didn’t state what the question was but I assume you want an equation.
Monthly Company charges: $12
Sign up fee: $20
Since we don’t know the amount of months represent this unknown variable with n.
Since $12 corresponds with the amount of months we will multiply $12 with n which make it: 12n. The sign up fee is not monthly so it’s additional.
Let the total cost be represented as T: the equation will be T = $12n + 20
Once again I don’t know what you are asking for, so if this is wrong or not what you are looking for I apologize.