15 CB || DA C B x F E 4 D 10 16 A

CB||DA, следовательно, треугольники CFE и DAE подобны по двум углам. Составим отношение сторон:

$$\frac{CF}{FD} = \frac{FE}{EA} = \frac{CE}{DA}$$
$$\frac{x}{4} = \frac{FE}{10} = \frac{CE}{16}$$
$$\frac{FE}{10} = \frac{CE}{16}$$
$$CE + FE = 14$$
$$10CE = 16FE$$
$$10CE = 16(14-CE)$$
$$10CE = 224 - 16CE$$
$$26CE = 224$$
$$CE = \frac{224}{26} = \frac{112}{13}$$
$$\frac{x}{4} = \frac{\frac{112}{13}}{16}$$
$$x = \frac{4 \cdot 112}{13 \cdot 16} = \frac{28}{13} \approx 2.15$$

Ответ: $$x = \frac{28}{13} \approx 2.15$$