how do i solve this

Well there is nothing to solve - I suppose you want to simplify it.

 

\((\sqrt5+\sqrt8)\times\sqrt{5+\sqrt{18}}\\ =(\sqrt5+2\sqrt2)\times\sqrt{5+3\sqrt{2}}\\\)

 

There really isn't a lot that you can do with this .

Simplify the following:
(sqrt(5)+sqrt(8)) sqrt(5+sqrt(18))

sqrt(18)  =  sqrt(2×3^2)  =  3 sqrt(2):
(sqrt(5)+sqrt(8)) sqrt(5+3 sqrt(2))

sqrt(8)  =  sqrt(2^3)  =  2 sqrt(2):
Answer: |  (sqrt(5)+2 sqrt(2)) sqrt(5+3 sqrt(2))