6.a. Write a BNF grammar that describes the structure of U.S. telephone numbers, which can be either (xxx)xxx-xxxx or xxx-xxxx, where x can be any digit from 0 to 9.b. Modify your grammar from Exercise 6a so that (1) the middle digit of an area code must be either a 0 or a 1, (2) the first digit of an area code cannot be a 0 or a 1, and (3) the firstdigit of the seven-digit phone number cannot be a 0 or a 1.c. Using your grammar from either Exercise 6a or 6b, show a parse tree for the phone number (612)555-1212.

Backus Naur Form (BNF): Syntax of the programming language is represented by using the notation called as Backus Naur Form (BNF). BNF grammar to describe the structure of U.S. telephone number <telephonenumber> is the non terminal object. The <telephonenumber> can be either (xxx)xxx-xxxx or xxx-xxxx and x can be any digit from 0 to 9. The BNF rule for <telephonenumber> is: Therefore, the above is a BNF grammar that describes the structure of a non terminal called <telephonenumber>. b) BNF grammar to describe the modified structure of telephone number <telephonenumber> is the non terminal object. The <telephonenumber> can be either (xxx)xxx-xxxx or xxx-xxxx and x can be any digit from 0 to 9. Second digit of the area code must be zero or one. First digit of the area code cannot be a zero or one. A seven digit phone number should not start with zero or one. The BNF rule for <telephonenumber> is: Therefore, the above is a BNF grammar that describes the modified structure of a non-terminal called <telephonenumber>.c) Parse tree for the telephone number (612)555-1212 : Parse tree is the representation of internal structure that starts with the individual token and ends with the desired goal using a grammar. Structure of the parse tree is: Root of the tree is the start symbol. Leaf node is the terminal object. Interior node is the non terminal object. Sentence appears in left to right direction of the leaves. Structure of the parse tree for the telephone number (612)555-1212 is shown below: Therefore, the above diagrammatic representation is the parse tree for the telephone number (612)555-1212 using the above BNF rule for <telephonenumber>.