Two circles of radii 15 cm and 10 cm intersect each other and the length of their common chord is 16 cm. What is the distance (in cm) between their centres?

$12 + 3 \sqrt {7}$ $15 + 2 \sqrt {161}$ $10 + \sqrt {161}$ $6 + \sqrt{161}$

$6 + \sqrt{161}$