18. Вычислите: 16/25 · (2/3 + 7/12) − 9/10 : 15/16.

\[\frac23+\frac7{12}=\frac8{12}+\frac7{12}=\frac54,\quad \frac{16}{25}\cdot\frac54=\frac45.\]

\[\frac9{10}:\frac{15}{16}=\frac9{10}\cdot\frac{16}{15}=\frac{24}{25}.\]

\[\frac45-\frac{24}{25}=\frac{20-24}{25}=-\frac4{25}.\]

Ответ: \(-\frac4{25}\).