д) 3,75:10,4=311:x 13 Решение:

$$3,75 : 10,4 = 3\frac{11}{13} : x$$

$$3,75 : 10,4 = \frac{375}{100} : \frac{104}{10} = \frac{15}{4} : \frac{52}{5}$$

$$3\frac{11}{13} = \frac{50}{13}$$

$$\frac{15}{4} : \frac{52}{5} = \frac{50}{13} : x$$

$$\frac{15}{4} \cdot x = \frac{50}{13} \cdot \frac{52}{5}$$

$$\frac{15}{4}x = \frac{50 \cdot 52}{13 \cdot 5}$$

$$\frac{15}{4}x = \frac{10 \cdot 4}{1} = 40$$

$$x = \frac{40}{\frac{15}{4}} = 40 \cdot \frac{4}{15} = \frac{40 \cdot 4}{15} = \frac{8 \cdot 4}{3} = \frac{32}{3} = 10\frac{2}{3}$$

Ответ: $$x = 10\frac{2}{3}$$.