Question

how did 5 came in the answer

Answer 1

as √ 9 (sqare of 3) +16 ( sqare of 4)
so √9+16
√25
5 which is root of 25

Answer 2

$\sqrt{3 {}^{2} } + \sqrt{4 { }^{2} } \\ \sqrt{9 + 16} \\ \sqrt{25 } \\ 5$
Hope this will help.