F(x)= x sqrt(x + 4). which intervals is it increasing and decreasing on? . which interval is it concave up?

A ) The domain : x ∈ ( - 4 , + ∞ )
f ` ( X ) =
f ` (  x ) < 0 
3 x + 8 < 0
x < - 8 /3
x < -2 2/3
f ( x ) is decreasing for : x ∈ ( - 4 ,  - 2  2/3  )
f ( x ) is increasing for: x ∈ ( -2  2/3,  + ∞ )
b ) f `` ( x ) = 
f `` ( x ) > 0:
3 x + 16 > 0
x > - 16/3
x > - 5 1/3
f ( x ) is concave up for x ∈ ( - 4 , + ∞ ) - the domain