The function is .

Here represents the monthly cost of international calls in dollars and represents number of minutes used.

(a)

Find the cost when number of minutes used .

Substitue in the function .

The monthly cost of international calls in dollars is is dollars.

(b)

Find the number of minutes when monthly bill of international calls is .

Substitute in the function .

The number of minutes is .

(c)

Find the maximum no.of minutes when the cost is .

 Substitute in the function .

The maximun number of minutes used is minutes.

(d).

Find the implied domain of , if there are days in the month.

The function , where number of minutes used can never be negative.

The month has days then total no.of minutes are

Hence the implied domain of is or .

(a) The monthly cost of international calls in dollars is is dollars.

(b) The number of minutes is .

(c) The maximun number of minutes used is minutes.

(d) Tthe implied domain of is or .