Nadia and Farid are stamp collectors. Each of them has 150 stamps in his or her album, made up only of 20-cent stamps and 60-cent stamps. Nadia has 18 more 60-cent stamps than Farid. Farid has 40 sixty-cent stamps in his album. Each 60-cent stamp weighs 3 g and each 20-cent stamp weighs 2 g. (a) Whose stamps are worth more in total value, and by how much? (b) What is the total weight of Farid's stamps, in kilograms?
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