Final answer:
Ona's average earnings over a four-week period, including salary and commission, is $1,815.
Step-by-step explanation:
To find Ona's average earnings, we need to determine the total earnings and then divide it by the number of weeks. Ona receives a salary of $1,500 per week, so the total salary for the four-week period is $1,500 x 4 = $6,000. Ona also receives a commission of 3% on all sales, so the commission on $42,000 worth of cars is $42,000 x 0.03 = $1,260. Therefore, Ona's total earnings for the four-week period are $6,000 + $1,260 = $7,260. To find the average earnings, we divide the total earnings by the number of weeks: $7,260 ÷ 4 = $1,815.