Answer
The distance between the two $B$ nuclei is $4.30\dot{A}$.
Work Step by Step
To find the bond length for the $A-B$ bond you must first find the atomic radii for $A$ and $B$. This is half the distance of the bond lengths for $A-A$ and $B-B$.
The atomic radii for $A$ is $2.36\div2=1.18$.
The atomic radii for $B$ is $1.94\div2=0.97$.
The bond length for $A-B$ is the sum of the two atomic radii.
$1.18+0.97=2.15$
Since the $B-A-B$ structure is linear, the distance between the two $B$ nuclei is twice the length of the $A-B$ bond.
$2.15\times2=4.30$
