Linear Function Problem! Please Help!?

An offshore oil rig is located at point A, which is 10 miles out to sea. An oil pipeline is to be constructed from point A to a point C on the shore and then to an oil refinery at point D farther up the coast. The distance from point B to point D is 50 miles. If it costs $8000 per mile to lay the pipeline in the sea and $2000 per mile on land, express the cost of laying the pipeline in terms of x, where x is the distance from B to C.