ok, so your equation would be 3d*5+d*10=100. multiply 3d times 5 and d times 10. that would give you 15d+10d=100. add 15d and 10d together you get 25d=100. divide 25d and 100 by 25 and that will give you d=4 therefore you have 4 dimes. multiply 4 times 3 and that will give you 12, therefore, you have 12 nickels.
