shorter PAC tranche, more protection protection, question, shorter

segalm

it says in the CFAI book, volume 5, p. 398, the degree of protection against contraction risk increases the shorter the pac tranche.

i'm a little confused here, first of all it says that the pac B tranche has a par amount of 8 mio and then in the test it mentionts 93 mio. what is the par amount or why they add 85+ 8? because for trance C they don't do that.

sorry, im a little confused here. the question at the end is, why does the shorter PAC tranche have more protection. and what is defined as shoerter?
Is PAC A tranche shorter than PAC-B tranche? does it also depend on the par amount?
thanks