At the Barber's

Algebra Level 2

You have two solutions of hydrogen peroxide: a $30$ % solution and a $3$ % solution and mix them to get a $12$ % solution. If the ratio of the required amount of the two solutions is found to be in the form $\frac{a}{b}$ , where $a$ and $b$ are coprime positive integers, then what is $a + b$ ?