GRE Big Book Test 1, Section 7, Q10

I’m sure this was asked before but I cannot find it. Can anyone provide some insight into this question?
temp

Since a* = 1 - a, you can just substitute the value of a with (-1) so for (-1)* = 1 - (-1) = 2
Thus, ((-1)*)* = 2* which is equal to the second quantity.

How did you get -1 out of 1-a?