3 2 10 15 -- --

$$\frac{3}{10} - \frac{2}{15} = \frac{3 \cdot 3}{10 \cdot 3} - \frac{2 \cdot 2}{15 \cdot 2} = \frac{9}{30} - \frac{4}{30} = \frac{5}{30} = \frac{1}{6}$$

Ответ: $$\frac{1}{6}$$