Linear equation with different variable on the denominator? I have this given problem. That asking me to solve for $x$. Although this example has answered. I've had troubles on a certain part.
Here's the equation with answer

\begin{align*}
\frac{2x-a}b &= \frac{4x-b}a\\
a(2x-a) &= b(4x-b) \\
2ax-a^2 &= 4bx - b^2 \\
2ax-4bx &= a^2 - b^2 \\
x(2a-4b) &= a^2 - b^2 \\
x&=\frac{a^2-b^2}{2a-4b}
\end{align*}

How did we arrive to 
$$a(2x -a) = b(4x-b)?$$

The process done is called Cross-multiplication.
This technique is generally used to work faster, we can solve such problems in 1 step rather than 2.
Let's say we have the following equation:
$$\frac{a}{b}=\frac{c}{d}$$
We can do it this way, without cross-multiplication:
Multiply both sides by $b$:
$$a=\frac{c}{d} b$$
Multiply both sides by $d$:
$$ad=bc$$
Now, let's use cross-multiplication:
$$\frac{\color{red}a}{\color{blue}b}=\frac{\color{blue}c}{\color{red}d}$$
We multiply the red and blue terms only.
$$\color{red}{ad}=\color{blue}{bc}$$
Now apply the same technique to the equation in your picture, and you should get the answer you were looking for.
