If the calibration curve is a straight line, it must follow the general form, y=mx+b. Thus, the equation must be: A = 0.0182x + 0.007. The corrected absorbance is:
Corrected Absorbance = 0.308 - 0.072 = 0.236
Substitute this to the formula to find x.
0.236 = 0.0182x + 0.007
Solving for x,
x = 12.58
Thus, the concentration of the protein at this absorbance is 12.58 μg.