(Look at image first before reading explanation!!)
Keeping in mind that this is all underneath the cube root:
Separate 6^4 to into (6^3)(6^1)
The cube root cancels the power of 3 on 6^3 therefore it can be moved outside of the radical.
As for 6^1, anything to the power of 1 is itself, so 6^1=6. Nothing else can be simplified so you are left with the answer in the image attached.
Hope this helps!
