b) 1/2x + 1/8x = 3/4

* Hướng dẫn giải

$\begin{array}{l}\mathrm{b}) \frac{1}{2}\mathrm{x}+\frac{1}{8}\mathrm{x}=\frac{3}{4}\\ \mathrm{x}\left(\frac{1.4}{2.4}+\frac{1}{8}\right)=\frac{3}{4}\\ \mathrm{x}\left(\frac{4}{8}+\frac{1}{8}\right)=\frac{3}{4}\\ \frac{5}{8}\mathrm{x}=\frac{3}{4}\\ \mathrm{x}=\frac{3}{4}:\frac{5}{8}\\ \mathrm{x}=\frac{3}{4}.\frac{8}{5}\\ \mathrm{x}=\frac{6}{5}\end{array}$