Task: Question Answering
Input (English): Problem: working simultaneously and independently at an identical constant rate, 5 machines of a certain type can produce a total of x units of product p in 4 days. how many of these machines, working simultaneously and independently at this constant rate, can produce a total of 2 x units of product p in 2 days ?
Options: a. 11, b. 13, c. 15, d. 18, e. 20
Output (English): e