Transition from embryonic DNA to B-cell DNA?

[gigi]

The DNA for an H chain in a B cell making IgE antibody for Tularemia has the following structure: 5′-5'—V8—D4—J2—Cε—Cα2—3'. How many individual rearrangements were required to go from the embryonic DNA to this B-cell DNA?

I know IgM is the embryonic immunoglobin, so the rearrangements occur from that one. But I have no idea how you figure out which arrangements occur because can't there be thousands of possibilities for the IgM? Also I know IgE has an extra component on the H chain but doesn't IgM have an extra one as well or am I just imagining things?

My guess was 4 individual rearrangements but I'm definitely not sure if that's correct.