Question

This is the call plan for Robert's cell phone:

Answer 1

$0.20 times 30 minutes = $6.00
So $6.00 plus the $15 charge each month = $21.00

Answer 2

To answer this, first make an equation representing the data: 

15+ 0.20X= Bill

now plug in data you know:

15 + 0.20(30)= bill

and finally solve it: 
Bill= $21.00