iframe auto height

I am looking to create a simple set of 3 iframes like the diagram below with A and B being static in height and C is an autofit to the size of the window.

----------------------------
           A   (77px)
----------------------------
           B   (33px)
----------------------------


           C   (auto)


----------------------------

I am basically looking to replace old frame code that looked like this....
<body>
    <frameset rows="74,33,*" framespacing="0" border="0" frameborder="0">
          <frame src="A.asp" name="A" scrolling="no" noresize>
          <frame src="B.asp" name="B" scrolling="no" >
          <frame src="C.asp" name="C" scrolling="auto" >
    </frameset>
</body>

to iframes that look something like this...
<body>
<iframe name="A" width="100%" height="74" frameborder="0" scrolling="no" src="A.asp" ></iframe>
<iframe name="B" width="100%" height="33" frameborder="0" scrolling="no" src="B.asp" ></iframe>
<iframe name="C" width="100%" height="100%" frameborder="0" scrolling="auto" src="C.asp" ></iframe>
</body>


I cannot seem to get my height in frame C to work like it did with the traditional frameset where it would autofit to the size of the browser window.  Are there solutions to this?
Thanks,
Jon

201407-LO-Qu-007

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