Question: What is the length of the River which has Wild Horse Creek as a tributary ?

Related documents: [0]  [DOC] Powder River is a tributary of the Yellowstone River, approximately 375 mi long in northeastern Wyoming and southeastern Montana in the United States. It drains an area historically known as the Powder River Country on the high plains east of the Bighorn Mountains. [END] 
[1]  [DOC] Wild Horse Creek is a tributary of the Powder River in Wyoming. The USGS has a station on the creek, near Arvada. [END]  
Answer: 375 mi long
375 mi long