I am new to discrete math, and am having trouble with a couple problems..

What is the inverse of the following relations:

Rsub1 = {(a, b) | a < b}

Rsub2 = {(a, b) | a divides b}

Also, i need help with composition.. :

What is Rsub3 of Rsub4 if

Rsub3 = {(a, b) | a > b}

Rsub4 = {(a, b) | a >= b}