A string that is obtained by rearranging the letters of the word POOPERSCOOPER is called cool, if each occurrence of E has the letter R to its left or right, and each occurrence of R has the letter E to its left or right. Thus, both POOPERSCOOPER and OPRECSOOOERPP are cool, whereas EPOOPRSCOOPER is not cool. What is the number of cool strings? Select one: a) ( b • 6)-2 Od)-(-3 D