At weekends Paul and his family do different things. What are Paul and his family doing now? What do they usually do? Choose the correct verb forms. Underline them.

Пусть скорость течения реки х км\час. Тогда скорость катера по течению 12+х км\час, а против течения 12-х км\час. Составим уравнение:
45\(12+х) + 45(12-х) = 8
45(12-х)+45(12+х)=1152-8х²
8х²=72
х²=9
х=3
ответ: 3 км\час.