You will be given a definition of a task first, then some input of the task.
In this task, you need to provide the correct option for a given problem from the provided options.

Problem: in a class , 30 students pass in english and 20 students in math , while some students among these pass in both . how many more students do only english as compared to those doing only maths ?
Options: a ) 10 , b ) 15 , c ) 20 , d ) 25 , e ) indeterminate
Output:
a