Write an equation for the cost $C$ of renting a bicycle for $t$ hours if the subscription fee is $7 and the rental fee is $2.50 per hour. $$\begin{aligned} \text{Cost}\amp = (\text{subscription fee})+(\text{hourly rate})\cdot(\text{number of hours}) \end{aligned}$$ $C=$$+$ $\cdot ~ t$