Hi, there-- Let n be the number of nickels. Let d be the number of dimes. The value of the nickels is 0.05 times the number of nickels, or 0.05n. The value of the dimes is 0.10 times the number of dimes. The value of the nickels plus the value of the dimes equal $8.50. In other words, 0.05n + 0.10d = 8.50 Hope this helps, Mrs. Figgy