Hey guys, My first post here, but basically I have this problem, and I can get the answer out, but I cheated to get the answer, my working out isn't quite correct.

I just can't work it out, I've gotten this far, but maybe I'm missing something so simple.

Anyhelp would be appreciated. I know what the answer is supposed to be, but I have a spare h left over and to get the 2*sqrt(3+5x) can't have the h there.