Final answer:
The sum of the lower limits of the modal class and the median class is 50.
Step-by-step explanation:
The lower limits of the modal class are 20-30 and the median class is 30-40. To find the sum of the lower limits, we need to add the lower limit of the modal class (20) and the lower limit of the median class (30). The sum is 20 + 30 = 50. Therefore, the correct answer is d) 50.