Final answer:
The unit rate of earning $105 for 12 1/2 hours of work is calculated by dividing $105 by 12.5, which equals $8.40 per hour. Thus, the correct answer is $8.40 per hour.
Step-by-step explanation:
To find the unit rate (dollars per hour) for earning $105 for 12 1/2 hours, we divide the total amount of money earned by the total number of hours worked. The unit rate is calculated as follows:
Total Earnings = $105
Total Hours Worked = 12.5 hours (since 12 1/2 hours is the same as 12.5 hours)
Unit Rate = Total Earnings / Total Hours Worked
Unit Rate = $105 / 12.5
Unit Rate = $8.40 per hour
Therefore, the correct answer is B. $8.40 per hour.