Question 893769
Another, much older help request showed the formula as {{{d=D(a+1)/24}}}.
See that post here: <a href="http://www.algebra.com/algebra/homework/NumericFractions/Numeric_Fractions.faq.question.391130.html">http://www.algebra.com/algebra/homework/NumericFractions/Numeric_Fractions.faq.question.391130.html</a>


Your problem is given a=9 years, and D=500 mg.
Substitute the values and evaluate d.


{{{d=500(9+1)/24}}}
{{{d=5000/24}}}
{{{highlight(d=208)}}} mg or to whatever accuracy seems to make sense.