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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def equation(operation, firstnum, secondnum):
 """ Solve a simple maths equation manually """

    if operation == 'plus':
        return firstnum + secondnum
    elif operation == 'minus':
        return firstnum - secondnum
    elif operation == 'multiply':
        return firstnum * secondnum
    elif operation == 'divide':
        if not secondnum == 0:
            return firstnum / secondnum
        raise ZeroDivisionError("Unable to divide by 0.")
    raise ValueError('Invalid operation provided.')