Refer to the Following Ages (Rounded to the Nearest Whole

Refer to the following ages (rounded to the nearest whole year) of employees at a large company
That were grouped into a distribution with class limits:
20 up to 30
30 up to 40
40 up to 50
50 up to 60
60 up to 70
What is the class interval and the midpoint of the first class?

A) 20 and 25
B) 20 and 24.5
C) 10 and 25
D) 10 and 24.5