Manipulating list in order to interpolate

[grduran12]

So I'm trying to create a program able to interpolate from a list of values (more like a matrix) where the left column correspond to the value A and the right column to the value F(A) and so on, then if I'm interest on the value F(B) knowing B the program should do a linear interpolation between F(A) and F(C), I'm not familiar with programming on RPL I'm used to visual so I hope you guys can give me some hints so I'll do it myself.

Additional info:
I've a HP50g
I'm writing my codes on HPuseredit 6