What is the difference, in dollars, between the cost of the Unlimited Talk Plan and the total cost for 1,420 minutes with plan C?

Answer:
The difference is $10
Step-by-step explanation:
we know that
The cost of the Unlimited Talk Plan is $99.99 per month
The total cost for 1,420 minutes with plan C is equal to
$79.99+(1,420-1,400)*$0.50=$89.99
The difference is equal to
$99.99-$89.99=$10