Dixon and his little sister Ariadne stand next to each other on the playground on a sunny afternoon. Their mother measures their shadows. Dixon's shadow is
feet long and Ariadne's shadow is
feet long. If Dixon is
feet tall, how tall is Ariadne?

An image shows Dixon and Ariadne standing next to each other. Dixon forms a right triangle with a line going from the end of his shadow to the top of his head. The base of the triangle is 18 feet. The height of the triangle is 6 feet. Ariadne forms a right triangle with a line going from the end of her shadow to the top of her head. The base of the triangle is 15 feet. The height of the triangle is unknown.

Ariadne is blank feet tall.

The solution is