To represent the total cost for the cellphone data plan, we can create an expression that includes both the one-time startup fee and the ongoing monthly charges.
The total cost \( C \) for \( m \) months with a monthly fee of $55 and a one-time startup fee of $21 can be expressed as:
\[ C = 21 + 55m \]
Now, to calculate the total cost for 6 months, we substitute \( m = 6 \) into the expression:
\[ C = 21 + 55(6) \]
Calculating this:
\[ C = 21 + 330 \] \[ C = 351 \]
Therefore, the total cost for 6 months is $351.