This is a system of equations problem. Let x be the number of dimes and y be the number of nickels.
From the problem, we know the following:
x + y = n (where n is the total number of coins)
y = 3x - 9 (because the number of nickels is three times the number of dimes minus nine)
We also know that the total value of the coins is $2.55 and that a dime is worth $0.10 and a nickel is worth $0.05. So we can create an equation using the total value of the coins:
0.10x + 0.05y = 2.55
Now we have a system of three equations and three variables. To solve for x, y and n, we can use substitution or elimination method.
First equation and second equation:
x+3x-9 = n
4x-9=n
4x = n+9
x = (n+9)/4
By substituting the value of x in equation 3
0.10*(n+9)/4 + 0.05*(3*(n+9)/4-9) = 2.55
Solving this equation we get n = 63
Thus, x = (63+9)/4 = 18 dimes
y = 3x - 9 = 3*18 - 9 = 45 nickels
So, Carolyn has 18 dimes and 45 nickels.