Use the Chain Rule.
I'm no expert at this (posted a chain rule question yesterday actually) but I think you want to take dy/du of 4u^1/2 and du/dx of u=(sec x + tan x) and multiply. Then substitute (sec x + tan x) back into the equation for u.
I'll stick around for the answer to this question because I'm not confident in my work. When I try to solve I get an ugly answer, which may be true...but I'm not sure.