Answer:
b = 36 is the lie.
Step by step:
If we plug in b with it equaling -36 the equation will be
-39 - (-36) which you remove the minus from the -36 and change the subtraction to addition and you get
-39 + 36 = -3
In the end b = -3
So the other one must be wrong, but just incase we will plug it in.
-36 - 36 = 0
Plugging in 36 for b results in 0 which is not correct.