Two sides of a triangle have lengths 10 and 15 . The length of the altitude to the third side is the average of the lengths of the altitudes to the two given sides. How long is the third side?

**Answer Choices**

A. 6

B. 8

C. 9

D. 12

E. 18

Two sides of a triangle have lengths 10 and 15 . The length of the altitude to the third side is the average of the lengths of the altitudes to the two given sides. How long is the third side?

**Answer Choices**

A. 6

B. 8

C. 9

D. 12

E. 18