Cubic Roots

[scantor]

Looking for help in finding cubic roots.

Please open attachment. The attached data uses a cubic spline to define the curve. There are 6 points, hence 5 sets of spline coefficients.

I need to find the root when y = 0.2656.

There must be VB code or Add-In that performs, what should be an easy task.

Thanks,

Sheldon S. Cantor