Kevin has $4.85 in nickels and dimes. If he has 34 fewer dimes than nickels, how many coins (nickels and dimes) does he have altogether?

Value of nickel * number of nickels + Value of dime * number of dimes = 4.85

.05 * (N) + .10 ( N - 34) = 4.85

.05N + .10N - 3.4 = 4.85

.15N = 4.85 + 3.4

.15N = 8.25

N = 8.25 / .15 = 55 = number of nickels

N - 34 = 55 - 34 = 21 = number of dimes