sorry pls ignore this answer
but I think it's 10
[tex]\\ \sf\longmapsto \sqrt{5 {ab}^{2} } \\ \\ \sf\longmapsto \sqrt{5 \times 5 \times {2}^{2} } \\ \\ \sf\longmapsto \sqrt{25 \times 4 } \\ \\ \sf\longmapsto \sqrt{100} \\ \\ \sf\longmapsto 10[/tex]
