In this task, you need to answer the given multiple-choice question on the physics. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

[EX Q]: Problem: 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 weights 8 g / cm cube , then find the weight of the pipe . 
Options: ['a ) 3.696 kg', 'b ) 3.686 kg', 'c ) 2.696 kg', 'd ) 2.686 kg', 'e ) none of these']
[EX A]: a

[EX Q]: Problem: a rower can row 5 km / h in still water . when the river is running at 2 km / h , it takes the rower 1 hour to row to big rock and back . how many kilometers is it to big rock ? 
Options: a ) 1.5 , b ) 1.8 , c ) 2.1 , d ) 2.4 , e ) 2.7
[EX A]: c

[EX Q]: Problem: stacy and helon are 30 miles apart and walk towards each other along the same route . stacy walks at constant rate that is 1 mile per hour faster than helon ' s constant rate of 5 miles / hour . if helon starts her journey 24 minutes after stacy , how far from the original destination has helon walked when the two meet ? 
Options: a ) 5 miles , b ) 8 miles , c ) 6 miles , d ) 13 miles , e ) 12 miles
[EX A]:
d