Answer:
The answer is A
Explanation:
The installment plan she will probably choose is a down payment of $50 and monthly payments of $40 for 12 months.
In the a real scenario, multiplying the installment amount of $40 with the total month of 12 then adding it answer with the down payment of $50 should arrive at the cost of $500 of the phone but it doesn't. However, the option A, has the figure closet to the initial cost of $500.
The cost by choosing the option A is $530 so it is assumed that the $30 extra is the interest attached to the elongated period of payment.