= Solution
\b[One <fluorine-19 NMR> resonance, integrating to three equivalent <fluorine> nuclei, appears as a doublet of doublets with $J=6.6$ and $1.8\,\mathrm{Hz}$.] This predicts four principal lines of equal intensity, from coupling to $\mathrm H_a$ and $\mathrm H_b$, respectively. Relative to the unknown resonance centre, their offsets are $\pm4.2$ and $\pm2.4\,\mathrm{Hz}$.
Equivalent <fluorine> nuclei do not split one another. This prediction assumes ordinary <proton>-coupled acquisition; <proton decoupling> would collapse these four principal lines to a singlet. The proton and carbon spectra do not determine the numerical <fluorine> <chemical shift>. Weak natural-abundance <carbon-13> satellites could accompany the principal pattern.
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