If x is a string, then xr is the reverse of the string. for example, if x = 1011, then xr = 1101. a string is a palindrome if the string is the same backwards and forwards (i. e., if x = xr). let b = {0, 1}. the set bn is the set of all n-bit strings. let pn be the set of all strings in bn that are palindromes.(c) determine the cardinality of p7 by showing a bijection between p7 and bn for some n.