Bitcoin 24 API

Basically what I'm looking for is a reliable API that allows for the conversion of an imputed currency amount such as USD/Euro amount and a conversion would be made that would convert the amount to BTC.

I want to also point out that I am not looking to convert hard cash for actual bitcoin. I am only looking to determine the current value conversion of a particular USD/Euro at that particular time period.

I am hoping to use this feature on a current website (HTML/PHP/ETC..) that I am working on.

If anyone can point me to a reliable API that can perform such a task please let me know. Also if you happen to have any guides in regards to implementing/using the API that would also be greatly appreciated.

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