Question 44354
The 4th root of 16 is the square root of the suare root of 16:
{{{-sqrt((sqrt(16)))}}}
the square root of sixteen is 4, so:
{{{-sqrt((sqrt(16)))=-sqrt(4)}}}
{{{-sqrt(4)}}}
the square root of 4 is 2, so the solution to your problem is "-2". This is an integer (a whole number with no decaimals), and hence is a rational number,

I hope this helps. 
P.S. I am currently constructing my own homework help website for maths and physics. I would be extremely grateful if you would e-mail me some feedback on the help you recieved to adam.chapman@student.manchester.ac.uk
Adam