\[\boxed{\mathbf{1234\ (1234)}\mathbf{.}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[\angle ABF = \angle ABK + \angle KBF\]
\[\angle ABK = 90{^\circ}\]
\[\angle KBF = 180{^\circ} - (54{^\circ} + 90{^\circ}) =\]
\[= 180{^\circ} - 144{^\circ} = 36{^\circ}\]
\[\angle ABF = 90{^\circ} + 36{^\circ} = 126{^\circ}.\]
\[Ответ:\ \angle ABF = 126{^\circ}.\]