# Question 24dc7

Apr 6, 2017

$C = r + s \left(t - 3\right)$

#### Explanation:

The cost $C$ of the call will be $r$ cents for the initial 3 minutes plus the time $t$ multiplied by the rate $s$.

Since you have already paid for the first three minutes, that time will need to be deducted from the overall time $t$ before it is multiplied by the rate $s$.

So if $t > 3$, your cost will be: C=r+s(t-3)

Example: t=5, r=$3, s=$2

C=$3+$2(5-3) = $3+$2xx2 = $3+$4 = \$7