Subtract 2D curves at y axis values

Hi there,

I have three curves, but for simplicity, consider two curves: A of Xa and Ya data and B of Xba and Yb data, that has different sizes and an equal ultimate Ya and Yb. Using "intrep2" made them of equal length. Now I want to subtract (Xa-Xb) at every Ya that is the nearest to any Yb, i.e, lookup for Ya at Yb, then subtract X values of those points. Subtracting A-B will not work because Y values are of diffirent threshold. The following pictures shows my three curves:

I want to subtract the red from the others which would make them shift to the left with slight change in their slope. the (A-B) results the following:

here, black and blue curves should be at Zero or very close to it at all the X values, because (A-B) will also subtract the Y values,,

Best

Yose