The common band in the plasmid Eco/Bam digests is this one (A). It is the 3416 bp pGT4 fragment, present in all Eco/Bam digested clones (and of course in the pGT4 digest; lane 2).

About the inserts:
The top band in laan 6 (the insert of recombinant 3) must contain the 15721 bp Eco/Bam fragment of Lambda DNA, when you compare its migration rate with the fragments in lane 1 (see B).
In the same way, it's clear that the 2752 bp insert is in lane 5 (C), the 1868 bp insert in lane 7 (D), and the 1120 bp insert in lane 4 (E).
In lane 8, the insert (f) is not much separated from the vector part (lane 8 in A), so it is most probably one of the 3758/3775 bp inserts, which are present in the marker lane as a double band (g).

The two end fragments in lane 1 (H) are present in very low amounts, since apparently, most of these molecules have joined (by forming the cos-site) to end up in the 9035 bp band (I).

Lane 3 is the first digest for the additional experiment of groups B, which means cutting the two Hind III sites in the insert of pGTλ3758. It gives two fragments (J), both containing a part of the insert. The bigger one (K) contains also the entire vector part.

In lanes 2 and 3 a very low amount of partial digestion product is visible (L). In lane 2 those molecules contain still an intact BamHI or EcoRI site, and in the lane 3 partial band, still one of the two HindIII sites is intact..