<PRE><B>Question 104407</B>
12 bills total
$5 and $10 bills possible
$100 total
Let F be the number of $5 bills and T be the number of $10 bills. 
1.{{{F+T=12}}}Bill total equation. 
2.{{{5*F+10*T=100}}}Value equation.
Use equation 1 to solve for T and substitute into equation 2. 
 1.{{{F+T=12}}}
{{{T=12-F}}}
2.{{{5*F+10*T=100}}}
{{{5*F+10*(12-F)=100}}}Value equation.
{{{5F+120-10F=100}}}Distributive property.
{{{-5F+120=100}}}Simplify.
{{{-5F+120-120=100-120}}}Additive inverse of 120.
{{{-5F=-20}}}Multiplicative inverse of (-5). 
{{{F=4}}}Number of $5 bills.
{{{T=12-F=8}}}Number of $10 bills.
Number of $5 bills is 4.
Number of $10 bills is 8. </PRE>