20. Упростите: 16x × (−8/15 b) × (45/64).

\[16x\cdot\left(-\frac{8}{15b}\right)\cdot\frac{45}{64}=-\frac{16\cdot8\cdot45}{15\cdot64}\cdot\frac{x}{b}=-6\cdot\frac{x}{b}=-\frac{6x}{b}.\]

Ответ: \(-\frac{6x}{b}\).