One of the formulas for calculating the correct dosage for a child is as follows: c= a/(a+12) ∙ 180
c = child’s dosage in milligrams a = age of the child a = adult dosage in milligrams
what is the prescribed dosage of a certain medicine for a child 6 years old, if the adult dosage of the medicine is 180 milligrams?

I'm assuming you're formula is "C=a/(a+12)*A" as that is only logical

You get the formula "C=a/(a+12)*A"

You insert the numbers given, in place of the letters given.

C=6/(6+12)*180
C=3*180
C=540 mg

Which is of course wrong because it is more than the adults dosage. What i'm trying to say is "Your formula is incorrect , follow the steps I gave, but use the correct formula"