How many strings of 11 english letters are there

(a) If letters can be repeated

If no letters can be repeated

(b)Those start and end with the letter A, if letters can be repeated.

(c)Those start and end with the letters ST ( this order)if letters cannot be repeated.

(d)Those start and end with the letters ST Cin this orderifletters can be repeated.

(2) Discuss any two graphical representations of relations, Also prove that complex number

satisfies the equivalence Relation