eval function

I'm trying to do the following:

1) In the axiom command line, I enter a ponynomial: f:=-(37/84)*x^2 -  
(7/12)*x -1/42
2) Find the roots: x12:=radicalSolve(f,x)
3) Trying to evaluate the polynomial 12x^3 + 5x^2 + 11x + 16:
	g:=12*x^3 + 5*x^2 + 11*x + 16
	eval(f,x,x12.1)

Then I get the error:
    There are 15 exposed and 1 unexposed library operations named eval
       having 3 argument(s) but none was determined to be applicable.
       Use HyperDoc Browse, or issue
                               )display op eval
       to learn more about the available operations. Perhaps
       package-calling the operation or using coercions on the arguments
       will allow you to apply the operation.

    Cannot find a definition or applicable library operation named eval
       with argument type(s)
                              Polynomial Integer
                                  Variable x
                          Equation Expression Integer

       Perhaps you should use "@" to indicate the required return type,
       or "$" to specify which version of the function you need.


Can somebody tell me how to convert the type of x12.1 to something  
that eval will do the work with?

thanks
G