Answer
-6, 1.6, $\sqrt 6$, $6^{3}$
Work Step by Step
-6 is obviously the least because it is the only one which is less than 0.
We need to convert the radical number and the powered number to numbers or decimals in order to compare them.
We have 1.6, $\sqrt 6$ $\approx$ 2.44, $6^{3}$=216. After that, we can easily see that 1.6 is less than 2.44 because 1<2 and 216 is obviously greater than 2.44 because 216 is a three-digit number but 2.44 is only a one-digit number.