Hi CJ

You wrote
<<1: Is this y=1.083333333x^4-7.3333333x^3+16.416667x^2-6.16667x+4 the
correct equation? This would be a polynomial equation with the largest
exponent of four.

Yes that's correct, a fouth order polynomial. I want to calculate the value
of "x" for a given value of "y" (in this example I am using y = 25)

also
<<by searching for "Numerical Recipes in C", then look for Chapter 5.
section 6 (Quadratic and Cubic Equations), pp 183 ff.

Yes I found this reference but once again I was way out of my depth
in a very short time. I'm starting to think that this is beyond my
mathematical capabilities which I admit are not very high. I only went
to grade 10 at school and that was 25 years ago.

Thanks for taking the time to post.
Martin