Question 160274
Let x=number of one-peso bills 
Let y=number of five-peso bills

1x+5y=106
x+y=42


then


system is:

x+5y=106
x+y=42

substracting:


4y=64 then y=16 and x=42-16=26

so he has 26 1-peso bills and 16 5-peso-bills