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: if 21 lines are drawn in a plane such that no two of them are parallel and no three are concurrent , then in how many points do they intersect ? 
Options: a ) 150 , b ) 170 , c ) 190 , d ) 210 , e ) 230
[EX A]: d

[EX Q]: Problem: if 20 typists can type 48 letters in 20 minutes , then how many letters will 30 typists working at the same rate complete in 1 hour ? 
Options: a ) 63 , b ) 72 , c ) 144 , d ) 216 , e ) 400
[EX A]: d

[EX Q]: Problem: a 600 meter long train crosses a signal post in 20 seconds . how long will it take to cross a 3 kilometer long bridge , at the same speed ? 
Options: a ) 4 min , b ) 2 min , c ) 8 min , d ) 9 min , e ) 5 min
[EX A]:
b