geometry
posted by bilal .
a bank teller has a total of 124 bills in fives and tens. the total value of the money is $840. how many of each kind does he have?

Let x = $5 bills and y = $10 bills
x + y = 124
x = 124y
5x + 10y = 840
Substitute 124y for x in third equation and solve for y. Insert that value into the first equation and solve for x. Check by inserting both values into the last equation. 
How does your problem relate to geometry?