young's rule, upper ccequals=startfraction da over upper a plus 12 endfraction da a+12, can be used to approximate the dosage of a drug prescribed for children. in this formula, aequals=the child's age, in years, dequals=an adult dosage, and upper c equals thec=the proper child's dosage. use this formula to solve the problem. when the adult dosage is 10001000 milligrams, a child is given 500500 milligrams. what is that child's age?