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

Example Input: Problem: two trains of equal length are running on parallel lines in the same directions at 46 km / hr . and 36 km / hr . the faster trains pass the slower train in 144 seconds . the length of each train is : 
Options: a ) 82 m , b ) 150 m , c ) 172 m , d ) 200 m , e ) none of these
Example Output: d

Example Input: Problem: the element being searched for is not found in an array of 100 elements . what is the average number of comparisons needed in a sequential search to determine that the element is not there , if the elements are completely unordered ? 
Options: a ) 25 , b ) 50 , c ) 75 , d ) 100 , e ) 125
Example Output: d

Example Input: Problem: if x / 4 years ago roger was 21 years old and x / 4 years from now he will be 4 x years old , how old will he be 5 x years from now ? 
Options: a ) 32 , b ) 35 , c ) 30 , d ) 40 , e ) 70
Example Output:
e