Answer:
21.37 days.
Explanation:
Step 1
Find the total amount Nancy is paying for her iPhone
Cost of the phone = $899
Tax = 8.50%
Amount paid for tax = 8.5% × 899
= 8.5/100 × 899
= $76.415
Total amount Nancy is paying = Tax + Cost of the phone
= $76.415 + $899
= $975.415
Step 2
We are told in the question that Nancy had already saved $78
Hence, Totally amount left for Nancy to buy her iPhone = $975.415 - $78
= $897.415
Step 3
Nancy works at a car wash and earns $42 every day.
The number of days left for her to work in the car wash in order to buy her phone is calculated as:
$42 = 1 day
$897.415 = x days
Cross Multiply
= $42 × x = $897.415 × 1 day
x = $897.415/$42
x = 21.36702381 days.
Approximately, x = 21.37 days
Therefore, Nancy has to work for 21.37 days at the car wash to have enough money for her iphone