A parcel service wants to establish a weight value c, beyond which there will be an additional charge. The weight of parcels handled by this service is normally distributed with a mean of 6.4 kg and a standard deviation of 3 kg.

a.) What value for c (in kg) will insure that only 2.5 % of handled packages are assessed the additional charge? 

b.) What value for c (in kg) will insure that only 1.0 % of handled packages are assessed the additional charge?