Rose counted her money and found that her 25 coins which were nickels, dimes, and quarters were worth $3.20. the number of dimes exceeded the number of nickels by 4. how many coins of each kind did she have?

N = number of nickles 
D = number of dimes = N+4 
Q = number of quarters 
= 25-N-D 
= 25-N-(N+4) 
= 21-(2N) 

Add the coins to get $3.20 
(N*$0.05) + (D*$0.10) + (Q*$0.25) = $3.20 
Expressing D and Q in terms of N: 
(N*$0.05) + ((N+4)*$0.10) + (21-2N)*$0.25=$3.20 

Solve for N. Then plug N into the equations for D and Q