= Solution
Write the ordinary <structure factor> as $F_0=|F_0|e^{i\phi}$ and use $F=F_0+19.2i$. The intensities imply
$$
|F_0|=\sqrt{13130}=114.59,\qquad
15430=13130+19.2^2+2(19.2)|F_0|\sin\phi.
$$
Consequently $\sin\phi=0.43893$, and the two possible ordinary phases are
$$
\boxed{\phi\simeq26.0^\circ\quad\hbox{or}\quad154.0^\circ.}
$$
The twofold ambiguity is expected from a single anomalous-intensity constraint. The calculation assumes that the specified imaginary increment is the only change requiring inclusion; an additional unspecified real dispersive change could not be reconstructed from these data alone.
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