4) $$\frac{3}{8} : (-\frac{15}{45}) = \frac{3}{8} \cdot (-\frac{45}{15}) = \frac{3}{8} \cdot (-3) = -\frac{9}{8} = -1\frac{1}{8}$$
Ответ: $$-1\frac{1}{8}$$