Given the equation:
$$\frac{x - 12}{x - 4} = \frac{3}{5}$$
Multiply the equation sides by the denominator -4 + x
we get:
$$x - 12 = \frac{3 x}{5} - \frac{12}{5}$$
Move free summands (without x)
from left part to right part, we given:
$$x = \frac{3 x}{5} + \frac{48}{5}$$
Move the summands with the unknown x
from the right part to the left part:
$$\frac{2 x}{5} = \frac{48}{5}$$
Divide both parts of the equation by 2/5
x = 48/5 / (2/5)
We get the answer: x = 24