Question 20966
This is a two step problem.  First, you must write expressions denoting the amount of five and ten dollar bills.  Second, you must write an equation that shows the relationship between the expressions and the dollar amount.


x=number of ten dollar bills
2x=number of five dollar bills


$10(x) + $5(2x) = $660
10x + 10x = 660
20x = 660
x = 33


There are 33 $10 bills and 66 $5 bills.  I hope that you were able to follow the solution.