Final answer:
After calculating Madeline's earnings from babysitting and her remaining needed earnings, we find that she must work a minimum of 9 whole hours washing cars to meet her target of $120, provided she works no more than 15 total hours. Since 9.2 hours is not a whole number, we round up to the next whole hour, which is 10 hours.
Step-by-step explanation:
To determine the minimum number of whole hours Madeline must work washing cars, we calculate as follows:
Madeline earns $7 per hour babysitting and has worked 4 hours, so her earnings from babysitting are 4 hours * $7/hour = $28.
To meet her requirement of earning at least $120 in a week, we subtract her babysitting earnings from her minimum required earnings: $120 - $28 = $92.
Since Madeline makes $10 per hour washing cars, we divide the remaining amount she needs by her car washing hourly rate: $92 / $10/hour = 9.2 hours.
Because Madeline can only work whole hours, and she needs to make at least $92 more, she must work at least the next whole number of hours, which is 10 hours. However, she has a limit of working no more than 15 hours total. Having already worked 4 hours babysitting, she can work up to 15 - 4 = 11 hours washing cars. Since she needs to work at least 10 whole hours washing cars to meet her earnings requirement of $120 and does not exceed her 15-hour work limit, the answer is D) 9 hours.