In this task, you need to answer the given multiple-choice question on the gain. Gain is the value by which to multiply the input. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Problem: i sold a book at a profit of 10 % . had i sold it for $ 150 more , 15 % would have been gained . find the cost price ? 
Options: a ) $ 2000 , b ) $ 2500 , c ) $ 3000 , d ) $ 3120 , e ) $ 1540
c

Problem: the area of a circle is increased by 1500 % . by what percent has the radius of the circle increased ? 
Options: a ) 100 % , b ) 200 % , c ) 300 % , d ) 600 % , e ) 800 %
c

Problem: a ball dropped from h height and moves 80 % of height each time . total distance covered is 
Options: a ) 4 h , b ) 5 h , c ) 7 h , d ) 9 h , e ) 8 h

d