1 120 pts] a) Write a grammar for the language consisting of strings that have n copies of the letter x followed by 2n copies of the letter y, where n o. For example, the string "xxyyyy" is in language but "xxyyy" and "yyx" are not. Explain why your grammar does the job. [10 pts b) Write the derivation and draw the parse tree for the sentence "xyyyyyy" as derived from the grammar of part a). [10 pts)