15-3b=63
subtract 15 from both sides
-3b=48
divide -3 from both sides
b= -16
Given: 

A.)Consider





Also,





Since, 
Therefore, both functions are inverses of each other.
B.
For the Composition function 
Since, the function
is not defined for
.
Therefore, the domain is 
For the Composition function 
Since, the function
is not defined for
.
Therefore, the domain is 