What wattage charging block does my MacBook Air need?

I seem to have lost the charging block that came with my MacBook Air model A2179. Is there a place where apple offers information (for example, a table?) where this kind of thing is posted? If not, does anybody know off the top of their head what charging block I need (e.g., 70Watt, 87 Watt, etc.)?

Thanks

[Re-Titled by Moderator]

Original Title: Finding charging block information