Final answer:
To find the percentage of earnings retained, divide the amount of earnings retained by the total earnings and multiply by 100. In this case, the percentage is 60%.
Step-by-step explanation:
To find the percentage of earnings retained, we need to divide the amount of earnings retained by the total earnings and then multiply by 100. In this case, the earnings retained are $72 million and the total earnings are $120 million. So, the percentage of earnings retained is (72/120) x 100 = 60%. Therefore, the correct answer is b) 60%.