When number of turns in a coil is trippled, without any

When number of turns in a coil is trippled, without any change in the length of coil, its self inductance becomes?

Self-inductance is proportional to the number of turns per unit length. The original self-inductance
(L) is given by

L =	μ_oπ(N)^2/r
	2

On tripling N, the new self-inductance becomes L

=	μ_oπ(3N)^2/r	= 9 ×		μ_oπ(N)^2/r
	2			2

= 9L