First process, use this rule for exponents to combine combine the two terms:
#x^color(red)(a) xx x^color(blue)(b) = x^(color(red)(a) + color(blue)(b))#
#(4^color(red)(6))(4^color(blue)(-8)) => 4^(color(red)(6) + color(blue)(-8)) => 4^color(red)(-2)#
Now, use this rule of exponents to rewrite the term to eliminate the negative exponent:
#x^color(red)(a) = 1/x^color(red)(-a)#
#4^color(red)(-2) => 1/4^color(red)(- -2) => 1/4^2 => 1/16#
Another process would be to use the second rule from above first:
#x^color(red)(a) = 1/x^color(red)(-a)#
#(4^color(red)(6))(4^color(blue)(-8)) => 4^color(red)(6)/4^color(blue)(- -8) => 4^color(red)(6)/4^color(blue)(8)#
Then use this rule of exponents to complete the simplification:
#x^color(red)(a)/x^color(blue)(b) = 1/x^(color(blue)(b)-color(red)(a))#
#4^color(red)(6)/4^color(blue)(8) => 1/4^(color(blue)(8)-color(red)(6)) => 1/4^2 = 1/16#
