Помогите а) 7:х=8:9 б)12:5=х:3 в)а:8=9:10 г)14:21=5:х дам 13 баллов

Решите задачу:

$1) \frac{7}{x} = \frac{8}{9} \\ x = \frac{7 \times 9}{8} = \frac{63}{8} \\ 2) \frac{12}{5} = \frac{x}{3} \\ x = \frac{12 \times 3}{5} = \frac{36}{5} \\ 3) \frac{a}{8} = \frac{9}{10} \\ a = \frac{8 \times 9}{10} = \frac{72}{10} \\ 4) \frac{14}{21} = \frac{5}{x} \\ x = \frac{21 \times 5}{14} = \frac{15}{2}$