Answer:
18
Step-by-step explanation
Let's say that the amount of 5 dollar bills is x and 20 dollar bills is y, with this we can make an equation
x + y = 24
With that we can say that
5x + 20y = 210
Because that is how much each bill costs and the amount of which will equal a total of 210
Solve this systems of equations using elimination
5x + 5y = 120
-5x - 20y = -210
-15y = -90
y = 6
Plug in y = 6 to the first equation.
x + 6 = 24
x = 18
18 is the amount of 5 dollar bills.
