In which of the following areas would it cost the least amount of money to build a barn?

beach

forests

mountains

plains

The areas which will cost the least amount of money to build a barn would be: Plains

Plains have the perfect amount of woods, water, and grass that will support the existence of a barn. Most barn animals cannot live in beach or mountains, so those options could be eliminated.

We need to spend more money to create space in forest if we want to build a barn there, so it could be eliminated too.