A DNA fragment has the sequence $5$'ATTACG$3\text{'}.$ Assuming standard biochemical conditions $($RT $=0\mathrm{.}6$ Kcal$/$mol$)$ and that $$Go$\text{'}$ for a Watson$-$Crick hydrogen bond is approximately $-0\mathrm{.}9$ kcal$/$mol$,$ calculate a best estimate for the dissociation constant for the helix association reaction:

DNA sequence fragment $+$ complementary DNA sequence fragment $----->$ DNA helix