4. A source emits letters from an alphabet A= {a,,a,,a3,a,,as) with probabilities Pla,) 0.15. Pla,) = 0.04. P(a) = 0.26. P(a4-0.05, and P(as) = 0.50. (a Calculate the entropy of this source. (e) Find the average length of the code in (b) and its redundancy