The optical rotation of a sample of 2-butonal is measured to be a(obs)= -.35 . The specific rotation for pure (+)-2-butanol is [a]D=-13.52 ml/g dm. If the cell path length was .6dm and the concentration of 2-butanol in the same was 0.15g/ml, calculate the specific rotation and the percentage of the (+) and (-) isomers in your sample.