Answer:
Arc length (AB ) =  9 cm .
Step-by-step explanation:
Given : The circumference of C is 72 cm and The center angle is 45.
To find : What is the length of arc AB (the minor arc).
Solution : We have given that 
circumference of C = 72 cm.
The center angle  =  45.
Formula of arc length  =  .
.
We have circumference = 2 pi r
Substitute the values arc length  =  .
.
Arc length =   .
.
                  =  9 cm 
Therefore ,Arc length (AB ) =  9 cm .