you can find this by adding the amount of coins he counted in total (19 coins) and the total amount of coins he had (15), the subtract 15 from 19 which will give you 4, this means that in both times he counted coins, only 4 of those coins in both counts were the same, and if you see, they mention dimes twice in both counts, this means the 4 coins that are shared between both counts are dimes, then dubstract 4 from 9, that's 5 so it's the 5 quarters, and substract 4 from 10 which will give you the 6 nickles
