Treatmnet of foriegn exchange differences

Dear Friends, 

I would like to know how the differences in foriegn currency transactions need to be accounted and disclosed in the following cases?

1. Sale in 2014 in usd(Invoice) @ ??

2. On balance sheet Date @ ??

3. In 2015 received (part payment) in USD-Then How to caliculate Exchange difference? and remaining amount?

Thanking you in advance