Problem 2 [6pt] Consider the context free grammar: S -> + SS SS | x where x is a terminal for letter x, and a string "+x+*x+xxx. a) (2pt) Write down the rightmost derivation for the string. b) (2pt) Draw the concrete parse tree for the string. c) (2pt) Is this grammar ambiguous or unambiguous? If it is ambiguous, give an equivalent unambiguous grammar; otherwise, argue why 2b is the only parse tree in the grammar for "+x+*x+xxx