This question is one where the numbers don't add up. You should ask your teacher to show you how to work it.
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Let n, d, q represent the numbers of nickels, dimes, and quarters Landau has, respectively.
... d = 7n +3 . . . . . the number of dimes is 3 more than 7 times the number of nickels
... q = 2n -4 . . . . . the number of quarters is 4 less than 2 times the number of nickels
... 5n +10d +25q = 330 . . . . the total value of the coins is 330 cents
Using the first two equations to substitute into the last one, we get
... 5n +10(7n +3) +25(2n -4) = 330
... 125n -70 = 330 . . . . . . eliminate parentheses, collect terms
... n = 400/125 . . . . . . . . add 70, divide by 125
... n = 3.2
... d = 7·3.2 +3 = 25.4
... q = 2·3.2 -4 = 2.4
Landau has 3.2 nickels, 25.4 dimes, and 2.4 quarters.