[tex]\\ \sf\longmapsto \sqrt{10}\times \sqrt{15}[/tex]
[tex]\\ \sf\longmapsto \sqrt{10\times 15}[/tex]
[tex]\\ \sf\longmapsto \sqrt{2\times 5\times 3\times 5}[/tex]
[tex]\\ \sf\longmapsto \sqrt{5\times 5\times 6}[/tex]
[tex]\\ \sf\longmapsto 5\sqrt{6}[/tex]
None of the above should be 4th option