Giải thích các bước giải:

$\begin{array}{l} a)\,\frac{3}{{10}}.x + \frac{3}{5} = \frac{3}{2}\\  \Leftrightarrow \frac{3}{{10}}.x = \frac{3}{2} - \frac{3}{5}\\  \Leftrightarrow \frac{3}{{10}}.x = \frac{9}{{10}}\\  \Leftrightarrow x = \frac{9}{{10}}:\frac{3}{{10}}\\  \Leftrightarrow x = 3\\ b)\,5 - 2\left| {x + 1} \right| = 1\\  \Leftrightarrow 2\left| {x + 1} \right| = 5 - 1\\  \Leftrightarrow 2\left| {x + 1} \right| = 4\\  \Leftrightarrow \left| {x + 1} \right| = 4:2\\  \Leftrightarrow \left| {x + 1} \right| = 2\\  \Leftrightarrow \left[ \begin{array}{l} x + 1 = 2\\ x + 1 =  - 2 \end{array} \right.\\  \Leftrightarrow \left[ \begin{array}{l} x = 2 - 1\\ x =  - 2 - 1 \end{array} \right.\\  \Leftrightarrow \left[ \begin{array}{l} x = 1\\ x =  - 3 \end{array} \right.\\ c)\,\left| {x + \frac{1}{4}} \right| = \frac{5}{6}\\  \Leftrightarrow \left[ \begin{array}{l} x + \frac{1}{4} = \frac{5}{6}\\ x + \frac{1}{4} =  - \frac{5}{6} \end{array} \right.\\  \Leftrightarrow \left[ \begin{array}{l} x = \frac{5}{6} - \frac{1}{4}\\ x =  - \frac{5}{6} - \frac{1}{4} \end{array} \right.\\  \Leftrightarrow \left[ \begin{array}{l} x = \frac{7}{{12}}\\ x =  - \frac{{13}}{{12}} \end{array} \right.\\ d)\,{(\frac{1}{2})^x} = \frac{1}{{64}}\\  \Leftrightarrow {(\frac{1}{2})^x} = {(\frac{1}{2})^4}\\  \Leftrightarrow x = 4\\ e)\,\frac{{x + 4}}{{y + 7}} = \frac{4}{7}\,\,\,DK:\,y \ne  - 7\\  \Leftrightarrow \frac{{x + 4}}{{y + 7}} - \frac{4}{7} = 0\\  \Leftrightarrow \frac{{7(x + 4) - 4(y + 7)}}{{7(y + 7)}} = 0\\  \Rightarrow 7x + 28 - 4y - 28 = 0\\  \Leftrightarrow x = \frac{4}{7}y\\ Thay\,vào\,x + y = 22\,ta\,có:\\ \frac{4}{7}y + y = 22\\  \Leftrightarrow \frac{{11y}}{7} = 22\\  \Leftrightarrow y = 14(tm)\\  =  > \,x = 8\\ f)\,Đặt\,\frac{x}{5} = \frac{y}{7} = \frac{x}{2} = t\\  \Rightarrow \left\{ \begin{array}{l} x = 5t\\ y = 7t\\ z = 2t \end{array} \right.\\ Khi\,đó:\\ y - x = 48\\  \Leftrightarrow 7t - 5t = 48\\  \Leftrightarrow t = 24\\  \Rightarrow \left\{ \begin{array}{l} x = 120\\ y = 168\\ z = 48 \end{array} \right. \end{array}$

x=3 

sr mik ko làm nhìu :3