Using basic proportionality theorem
[tex]\\ \sf\longmapsto \dfrac{x}{10}=\dfrac{42}{15}[/tex]
[tex]\\ \sf\longmapsto 15x=42(10)[/tex]
[tex]\\ \sf\longmapsto 15x=420[/tex]
[tex]\\ \sf\longmapsto x=\dfrac{420}{15}[/tex]
[tex]\\ \sf\longmapsto x=28[/tex]
