Im not sure how to do these questions, can someone please show me? :)

1. A cylidrical boiler with an open top is to be built from stinless steel with a copper bottom. The prise of copper is five times the cost of stainless steel. Determie the most economical dimentions for the bouler if the volume is 5 pi m^3.

2. A cirtain species of bird nests on an island A, 5 km from the nearist point B on the straght mainland shorline.these birds area released from the banding point C on the shoreline, whitch is 13 km from point B. the birds instinktevly choose to fly partly along the shoreline to point D ad then accross the water in such a way as to minimize there expenditure. They use 1.3 times as much energy to fly accross the water as they do to fly accross the land, due to air current. Deturmine the distance DC correct to 1 decimal place.