Question 920975
Not knowing the value of a loony, this could give an inequality  (because of the limited nickels value) and then two equations in three unknowns.  Playing with the given values all in the head, if a loony is 1.00 dollar, then 6 loonies is $6.00, and that leaves remaining 0.25 dollars, which could be worth 5 nickels.  There are your 11 coins:  


6 loonies plus 5 nickes, making 11 coins, and value sum to $6.25.


I could not find a more formal arithmetic method.