First, use this rule for radicals to rewrite the expression:
#root(3)(color(red)(16a)/color(blue)(27)) => root(3)(color(red)(16a))/root(3)(color(blue)(27)) => root(3)(color(red)(8 * 2a))/root(3)(color(blue)(27)) => root(3)(color(red)(2^3 * 2a))/root(3)(color(blue)(3^3))#
Next, use this rule for radicals to rewrite the numerator:
#root(n)(color(red)(a) * color(blue)(b)) = root(n)(color(red)(a)) * root(n)(color(blue)(b))#
#sqrt(color(red)(2^3) * color(blue)(2a))/root(3)(3^3) =>#
#(root(3)(color(red)(2^3))sqrt(color(blue)(2a)))/root(3)(3^3) =>#
#(color(red)(2)sqrt(color(blue)(2a)))/3#
Or
#color(red)(2)/3root(3)(color(blue)(2a))#