To determine the cost of the app for \( m \) months, you need to account for both the joining fee and the monthly subscription fee.
- The joining fee is $2.
- The monthly subscription cost is $5 per month, so for \( m \) months, it would be \( 5m \).
Therefore, the total cost \( C \) for \( m \) months can be expressed as:
\[ C = 2 + 5m \]
So, the expression that represents the cost of the app for \( m \) months is \( 2 + 5m \).