$$\frac{1}{65}+\frac{2}{40} = \frac{2}{x}$$

$$ \begin{aligned} \frac{1}{65}+\frac{2}{40} &= \frac{2}{x}&& \text{multiply ALL terms by } \color{blue}{ 65\cdot40x }. \\[1 em]65\cdot40x\cdot\frac{1}{65}+65\cdot40x\cdot\frac{2}{40} &= 65\cdot40x\cdot\frac{2}{x}&& \text{cancel out the denominators} \\[1 em]40x+130x &= 5200&& \text{simplify left side} \\[1 em]170x &= 5200&& \text{ divide both sides by $ 170 $ } \\[1 em]x &= \frac{5200}{170}&& \\[1 em]x &= \frac{520}{17}&& \\[1 em] \end{aligned} $$

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