The question is:
>A reaction rate doubles when the temperature increases from 25C to 40C. Calculate Ea and >the frequency factor.

I found the activation energy to be 35.8 kJ using the two point form of the arrhenius equation. What I'm having trouble with is finding the frequency factor. I have two unknowns, k and A, and to me it seems like this is impossible to solve without knowing what the rate constant k is. All the examples in the book solves this problem graphically, but apparently you can solve this another way according to my teacher. 

The answer given for A is 1.9 * 10^6 but what method do you use to solve for this?