Найдите x в пропорциях:Чётн.

Решите задачу:

$\frac{3.25}{4x-1.9} = \frac{13}{0.4} \\ 13(4x-1.9)=0.4\cdot3.25\\ 52x-24.7=1.3\\ 52x=1.3+24.7\\ 52x=26\\ x= \frac{26}{52} \\ x= \frac{1}{2} \\=================\\ \frac{1 \frac{4}{5} }{2.5} = \frac{7.2}{6x+1} \\ \frac{\frac{9}{5} }{2.5} = \frac{7.2}{6x+1} \\ \frac{1.8 }{2.5} = \frac{7.2}{6x+1} \\ 1.8(6x+1)=7.2\cdot2.5\\ 10.8x+1.8=18\\ 10.8x=18-1.8\\ 10.8x=16.2\\ x=1.5\\=================\\$
$\frac{ \frac{3}{8} }{0.75} = \frac{0.6}{x-2.8} \\\\ \frac{ 0.375}{0.75} = \frac{0.6}{x-2.8} \\ 0.375(x-2.8)=0.6\cdot0.75\\ 0.375x-1.05=0.45\\ 0.375x=0.45+1.05\\ 0.375x=1.5\\ x=4$