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Since no material index is given I am assuming that the blanks Front Curve is the true front... Then place the Rx on the Optical Cross to find the powers in both meridians... Then use the Back Vertex power formula to figure out the curve needed for the back curve
Dback = Dpower - [Dfront / (1 - (Dfront * thickness/index))]
Generally, if neither a refractive index nor a center thickness is provided, you must assume that the calculations are for a thin lens and that the surfaces curves are provided in the index of the material. Fortunately for Del, this is just a simple toric transposition problem, similar to the earlier problems.