Suppose a source sends symbols from a three letter alphabet with X {a, b, c} and

Suppose a source sends symbols from a three letter alphabet with X Ɛ {a, b, c} and Pa = 1/ 2, Pb = 1/ 4, Pc = 1/ 4 are the source symbol probabilities.
(a) Determine the entropy of this source.
(b) Give a source code that has an average codeword length that matches the entropy.