Given
  The average daily balance is $15
 The  daily periodic rate = 0.06%
 The number of days in the cycle is 30
Find out the monthly finance charge.
To proof   
Let us assume that the monthly finance charge = x
As given in the question
The average daily balance = $15
 daily periodic rate = 0.06%, 
First convert 0.06% in decimal form

= 0.0006
Daily finance charge =  0.0006 × 15
                                    =  0.009
 number of days in the cycle is 30
now 
monthly finance charge
Than the equation becomes
x = 15 × 0.0006 × 30
x = 0.009× 30
x  = $0.27
Thus the monthly finance charge is $0.27
Hence proved