Question 1004300
The problem description is incomplete.  Sixty-four bills at $1 each is not $199 dollars!



--New Information--
- One-dollar bills and ten-dollar bills -


x for the $1 bills, y for the $10 bills
{{{system(x+y=64,x+10y=199)}}}


The description is meaningful if the solution for the system gives whole-number values for x and y.
{{{x+10y-(x+y)=199-(x+y)}}}
{{{x+10y-(x+y)=199-64}}}
{{{9y=135}}}
{{{highlight(y=15)}}}, and then x is very simple to find.


You CAN use strictly substitution method if you want.  The steps just shown were part of that method, but the intent was to show you why Elimination Method is often convenient.