Write an expression for the total cost (in dollars) of a call lasting t𝑡 minutes.

To write an expression for the total cost of a call lasting $t$ minutes, you need to establish the rate charged per minute (let's denote this rate as $r$ dollars per minute). The total cost $C$ can then be calculated using the formula:

$C = r \cdot t$

Explanation:

1. Rate Definition: The rate ($r$) is the cost incurred for each minute of the call.
2. Duration: $t$ represents the total minutes the call lasts.
3. Total Cost Calculation: By multiplying the rate by the duration of the call, you determine the total expenditure for the entire duration.

Final Expression:

If you have specific values for $r$ (the rate per minute), you can substitute that value into the expression to calculate the total cost for a call lasting $t$ minutes.