2 answers:
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The root 
can be converted into the power 
. Therefore we can rewrite the problem as 
and then follow the exponent rules about a power to a power, multiplying 1/2 and 3/4 together.
Thus the problem becomes
, which then can be turned into ![\sqrt[8]{10} ^{3x}](https://tex.z-dn.net/?f=%20%5Csqrt%5B8%5D%7B10%7D%20%5E%7B3x%7D)
, making the last option our answer.
Thus the problem becomes