<h3>
Answer: 6</h3>
=======================================
Work Shown:
1 liter = 1000 mL
3 liters = 3000 mL
I multiplied both sides by 3.
Divide that result over 500 to get 3000/500 = 6
So she'll need to buy 6 cartons.
-------
You could also solve like this:
(1 carton)/(500 mL) = (x cartons)/(3000 mL)
1/500 = x/3000
1*3000 = 500*x ... cross multiply
3000 = 500x
500x = 3000
x = 3000/500 .... dividing both sides by 500
x = 6
