Dan’s phone company charges a standard monthly fee and extra for extra for each minute of long distance. So the total cost each month is determined by the minutes.

20 + 0.05m

Step-by-step explanation:

The phone company charges a standard fee as well as a fee for every minute of long distance.

When no minutes are used, the cost is $20.  This means that the standard fee is $20.

For 10 minutes, the cost is $20.50.  The standard fee is $20.  This means that for ten minutes, $0.50 is charged.  For one minute, the charge is $0.05,

$20.50 - $20 = $0.50

$0.50/10 = $0.05

Dan's monthly cost is the standard fee plus the charge per minute.

20 + 0.05m