t : 0 -> 0.1 -> 0.2 -> 0.3 -> ... -> 1
x : 0 -> 10  -> 30  -> 80  -> ... -> 1230

what is 't' of distance '75' ? look up in table
not in range t = [0,0.1), not in range [0.1,0.2), in range [0.2,0.3)
linearly interpolate, t = 0.2 + (0.3-0.2)*(75-30)/(80-30)