I hope this helps you. The answer is c
We can seperate (3b³) into two different parts, the constant and the variable.
The constant (3) and the variable (b) can both be squared and multiplied to get the correct answer, so:
3² = 9
(b³)² = 
So, 
Answer:
C≈8.17cm
Step-by-step explanation:
C=2πr=2·π·1.3≈8.16814cm