Question: How to get the index of some elements?

I have two small questions: 1. Given a list L: L:=[false, false, true, true, FAIL,false]; and I want to get the positions of "FAIL" (in this case 5) and false (1,2,6). HOW could I get that? 2. Now, given another list Z with the same number of elements: Z:=[z1,z2,z3,z4,z5,z6]; I would like to replace the values of FAIL by 0 (zero). (in the way that Z became: Z:=[z1,z2,z3,z4,0,z6];) It is possible to do that without using "for do" commands? Thanks in advance, JJacques
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