Two solenoids, A and $B,$ are wound using equal lengths of the same kind of wire. The length of the axis of each solenoid is large compared with its diameter. The axial length of $A$ is seven times as large as that of B$,$ and A has seven times as manv turns as B$.$ What is the ratio of the inductance of solanoid $A$ to that of solennid $B?$

$49$

$1$

$\frac{1}{9}$

$\frac{1}{49}$