Computer Science - Automata Help

Do 1a, 1b, 1 c, 1d. Please show detailed well-written work so I can understand. Thanks

a) What is the least fixed point of the kleene closure operation, assuming the natural order of set-inclusion; i.e., of f(L)-L" b) Define the language of all positive integers (decimal and with no preceeding zeros) that are divisible by three using set-builder notation. (Hint: all such integers have digits that sum to a number divisible by three; e.g., 59898; 5+9+8+9+8-39; 3+9-12; 1+2-3) c) Give a regular expression for the language of all strings over alphabet {0, 1) containing at least one 1 d) Give a regular expression for the language of all strings over alphabet {0, 1) that have exactly three non-contiguous 1s. (I.e., two can be contiguous, as in 01101, but not all three, 01110.)