Step 1 :We are given a child's growth function as \(f(x)=20+47 \log (x+2)\), where \(x\) represents her age in years and \(f(x)\) represents the percentage of her adult height reached at age \(x\).
Step 2 :We are asked to find the percentage of the child's adult height attained by age 6. This can be found by substituting \(x=6\) into the given function.
Step 3 :Substituting \(x=6\) into the function, we get \(f(6)=20+47 \log (6+2)\).
Step 4 :Calculating the above expression, we get \(f(6) = 117.73375245895228\).
Step 5 :Rounding this to the nearest whole number, we get \(118\).
Step 6 :So, the child will have attained \(\boxed{118\%}\) of her adult height by age 6.