Answer :

Edufirst
(f o g o h)(x) = f { g [ h(x) ] }

Which means: apply first function h, then apply function g to the result, and finally apply  function f to the new result.

h(25) = √25 = 5

g(5) = 5  - 3 = 2

f(2) = 3(2) = 6.

Answer: 6