Doctors often prescribe the same drugs for children as they do for adults. If "a" is the age of a child and "D" is the adult dosage, then to find the child's dosage "d", doctors can use the formula

d = D(a+1)/24 (Cowling's rule) or d = 0.08aD (Fried's rule). For what age do the two formulas give the same child's dosage?

I know the answer is 1.1, but I don't know how to get to this answer not using a graphing calculator.