Hello, good evening, could you help me with these two problems of the topic "Optimization"

7. two points A and B are on the shore of a straight beach, 6 km apart, One point C is in front of B 3 km away from the sea. It costs $ 400 to lay 1 km of pipe on the beach and $ 500 at sea. Determine the most economical way to trace the pipe from A to C (not necessarily go through B).

The answer must be $ 3,300

4. A straight circular cylinder must contain V cm ^ 3 of soft drink and use the minimum possible amount of material in its construction.

(Considering that 1L = 1 dm ^ 3)

The answer should be: t = 3 / 10h