Реши пропорции x/15=4/5 2/x=6/7 8/9=x/27 10/23=4/x

Решите задачу:

$1)\quad \frac{x}{15} = \frac{4}{5} \; ,\; \; x= \frac{4\cdot 15}{5} =12 \\\\2)\quad \frac{2}{x} = \frac{6}{7} \; ,\; \; x= \frac{2\cdot 7}{6} =\frac{7}{3} =2\frac{1}{3}\\\\3)\quad \frac{8}{9} = \frac{x}{27} \; ,\; \; x= \frac{8\cdot 27}{9}=24\\\\4)\quad \frac{10}{23} = \frac{4}{x} \; ,\; \; x= \frac{4\cdot 23}{10} =\frac{46}{5}=9\frac{1}{5}\\\\\\P.S.\; \; \frac{a}{b} = \frac{c}{d} \quad \Rightarrow \quad a\cdot d=b\cdot c$