... we will output -1 as a sign of error as concentration will not be negative.

But there are random tests that expect a negative concentration, e.g.

    [37, 31], [6, 8], 1  =>   -3.4347826086956523
    [61, 1], [5, 4], 74  =>   -1301.6666666666667
    [14, 27], [1, 8], 5  =>   -1.0526315789473684

e.g. [2,2], [4,4]. Indicating 2 units concentration of this chemical will absorb 2 units of light and 4 units concentration of this chemical will absorb 4 units of light.

This example is ambiguous, both absorbance and concentration have the same values. It is not clear if the input format is (absorbance, concentration) or (concentration, absorbance).

In python points shuld be tuples, not lists.