Answer:
Step-by-step explanation:
If all were $5 bills, the total would be $35. It is $20 more than that. Each time a $5 bill is replaced by a $10 bill, the total goes up $5. Since the total is $20 higher, there must be $20/$5 = 4 such replacements.
There are 4 $10 bills and 3 $5 bills.