Write the regular expression for the following over {a,b} or {0,1}

Strings with exactly three occurrences of ba.

Strings with at most 3 occurrences of ba

L = { aⁿ b^m | m + n is even}

Set of all the strings with exactly 2 as over {a,b}

All the strings containing the substring ccc over the set {a, b, c}

set of all the strings when ever run of a has a length of 4 over {a,b, c}.