Subject: mathqa
Question: a hollow iron pipe is 21 cm long and its external diameter is 8 cm . if the thickness of the pipe is 1 cm and iron weighs 8 g / cm ^ 3 , then the weight of the pipe is :
Option: 
A: 3.696 kg
B: 3.6 kg
C: 36.9 kg
D: 36 kg
Answer: A