5.1 840

$${\frac{5}{8}} : {\frac{1}{40}} = {\frac{5}{8}} \cdot {\frac{40}{1}} = {\frac{5 \cdot 40}{8 \cdot 1}} = {\frac{5 \cdot 5 \cdot 8}{8 \cdot 1}} = 25$$

Ответ: 25