Ok, first, express the bottom as (x+1)^1/2.
Then use y=u/v to differenciate. So, y'=(vu'-uv')/(v^2):
u= 3x+1
v= (x+1)^1/2
u'=3
v'=1/2x1(x+1)^-1/2.
=1/2(x+1)^-1/2.
Then put it into the formula above and it should be right :)
(Hope I've done it right and helped!)