We can solve it through proportionality or ratios
Let lamps required to create 60signals be x
Now
[tex]\\ \sf\longmapsto 2:4=x:60[/tex]
[tex]\\ \sf\longmapsto \dfrac{2}{4}=\dfrac{x}{60}[/tex]
[tex]\\ \sf\longmapsto 4x=60(2)[/tex]
[tex]\\ \sf\longmapsto 4x=120[/tex]
[tex]\\ \sf\longmapsto x=\dfrac{120}{4}[/tex]
[tex]\\ \sf\longmapsto x=30[/tex]