Explanation:
The triangles are similar triangles.
The ratio of corresponding sides are equal.
let the unknown side = x
14/(15+x) = (14-4)/15
14/(15+x) = 10/15
[tex]\begin{gathered} \frac{14}{\mleft(15+x\mright)}=\frac{10}{15} \\ \text{cross multiply:} \\ 14(15)=\text{ }10\mleft(15+x\mright) \end{gathered}[/tex][tex]\begin{gathered} 210\text{ = 150 + 10x} \\ 210\text{ - 150 = 10x} \\ 60\text{ = 10x} \end{gathered}[/tex]
