The triangles given are similar; therefore, the ratio of their side lengths must be the same.
This means
[tex]\frac{5}{x}=\frac{4}{24}=\frac{3}{18}[/tex]
therefore,
[tex]\frac{5}{x}=\frac{4}{24}[/tex]
cross multipication gives
[tex]24\cdot5=4x[/tex]
Dividing both sides by 4 gives
[tex]x=\frac{24\cdot5}{4}[/tex][tex]x=30[/tex]
which is our answer!
