The mass per unit length of a non-uniform rod ( AB ) of length ( l ) varies as ( 1x ) where ( k ) is a constant and ( x ) is the distance at any point on the rod measured from end ( A ). The centre of mass of the rod from ( A ) is:
a) ( kl²3 )
b) ( 2kl²3 )
c) ( kl²4 )
d) ( kl²2 )