Radio station call signs, II Refer to Exercise 8.39. By

QUESTION:

Radio station call signs, II Refer to Exercise 8.39. By 1922, there were more applications for radio station licenses than the number of three-letter call signs available. A radio station in New Orleans applied for and was granted the call sign WAAB. (a) How many four-letter call signs start with the letter W? Show your method. (b) In fact, no call sign was permitted in which the same letter appeared three times in a row. (Th ats why the New Orleans station got WAAB, not WAAA.) How many fourletter call signs starting with W are possible with this restriction? Show your work. (c) How many four-letter call signs start with W or K and meet the restriction in (b)? Show your method.