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'.

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
d

Problem: a man rows his boat 75 km downstream and 45 km upstream , taking 2 1 / 2 hours each time . find the speed of the stream ? 
Options: a ) 6 , b ) 7 , c ) 5 , d ) 8 , e ) 9
a

Problem: in the xy - plane the point ( - 2 - 3 ) is the centre of a circle , the point ( - 2 , 1 ) lies inside the circle and the point ( 4 , - 3 ) lies outside the circle . if the radius r of the circle r is an integer then diameter ? 
Options: a ) 6 , b ) 10 , c ) 4 , d ) 3 , e ) 2

b