Решение:
$$6\frac{1}{7} : 3 = \frac{x}{38}$$
$$\frac{43}{7} : 3 = \frac{x}{38}$$
$$\frac{43}{7} = \frac{3x}{38}$$
$$3x = \frac{43 \cdot 38}{7}$$
$$3x = \frac{1634}{7}$$
$$x = \frac{1634}{7 \cdot 3}$$
$$x = \frac{1634}{21}$$
$$x = 77 \frac{17}{21}$$
Ответ: $$77 \frac{17}{21}$$