Africa's west coast and the eastern coast of South America.
Eastern Coast should be capitalized when it refers to a specific place. Only the names of specific continents should be capitalized.
North America
eastern
Yes you do, because it is a name of a specific place.
hihun
Australia is bordered by the Pacific Ocean on its eastern coast.
New England is in Maine and is on the Eastern coast of the USA.
The eastern coast of the US
Suffolk, England is on the eastern coast of Britain.
mountain
white