Question 74897
{{{ sqrt(81x^8y^12z^20) }}}

Remember that everything that leaves a square root is the number or variable the square root is squaring. 
{{{ sqrt((9^2)((x^4)^2)((y^6)2)((z^10)^2)) }}}

When an exponent is raised to a power, you simply multiply the current exponent by the power it is raised to. 
Example: {{{ ((x^2)^4)}}} is the same as {{{ x^8 }}}

Therefore, the final answer is:

{{{ 9x^4y^6z^10 }}}