How to get the a single constant value

I have a really simple problem yet I cannot find the solution.
I have a function that calculates the exchange rate between two currencies. The inputs are constants:
Dim Test As New CurrencyExchangeRate.CurrencyConvertor Dim Rate = Test.ConversionRate(CurrencyExchangeRate.Currency.EUR, CurrencyExchangeRate.Currency.USD)I have currency codes in my database listed as "EUR", "USD" etc. that I want to use in the function. Unfortunately the function requires a constant value like CurrencyExchangeRate.Currency.EUR instead of a string value called "EUR" How can I turn the value from the database into a usable value for the function?
I know it must be very simple but I cannot figure it out.
Thanks!

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