Telephone numbers are preceded by a 3-digit area code (e.g. 437). In the followingquestions, any digit from {0, 1, 2, 3, 4, 5, 6, 7, 8, 9) can be used unless otherwise stated.How many area codes are possible if:a. the first digit must be 1?b. the third digit must not be 4?c. the second and third digits must be the same?d. neither 1 nor 2 must be used?