26) B

The first ring has 6.
The second has 4 extra. (Total 6 but 2 are from the first ring).
The third has 4 extra. (Total 6 but 2 are from the second ring).
The fourth has 3 extra. (Total 5 but 2 are from the third ring).

Total so far = 6 + 4 + 4 + 3 = 17

2 carbons are present in the CH₃ groups and 1 is present in CO₂H group.

Total = 17 + 2 + 1 = 20