Two points define a line. Why have you listed four points? They do not lie on the same line.
If x = 0.3, y cannot be both 0.4 and 0.1, unless the line is vertical, and it can't be because the other points have different x values
find the equation of the line
0.3,0.4
0.4,0.3
0.1,0.2
0.3,0.1
2 answers
If you mean fit a line to the points by least squares or something, please say so.