Discrete structures please solve

1. (3 marks) How many strings of five uppercase English letters can we construct if the first letter must be either A or B or C, the last letter must be either X or Y or Z and a) the letters in the string may be repeated? b) the letters in the string must be distinct? Explain your answers. stant with A, or B, or c and eny with x or y or Z= Thereare 3333=729 Firstletter=3wayssecory=3waysthird=3ways3,3.3,3,3.3=729ways.forth=3fifth=3sitth=3