Susan has 8 more dimes than she has nickels in her pocket, is she has a total of $3.05, how many times does she have?

Let the number of nickels be x, the number of dimes is x+8
but
1 nickel=$0.05 
1 dime=$0.1
thus, the total amount Susan has will be:
0.05x+0.1(x+8)=3.05
0.05x+0.1x+0.8=3.05
0.15x=2.25
x=2.25/0.15
x=15
thus the number of nickels is 15
number of dimes is 15+8=23

The answer for you question is b