We know that Kari bought 3 quarts of milk. This is, she bought 6 pints of milk, as 1 quart is 2 pints.
Now, as 1 pint is 473.176 mm, we have that 6 pints are:
![6(473.176)mm=2839.06\operatorname{mm}]()
And as 1,000 mm are 1 liter, we just divide the value obtained by 1,000. Thus,
![2,839.06\operatorname{mm}\cdot\frac{1l}{1,000\operatorname{mm}}=2.83906l]()
This means that Kari bought approximately 2.84 liters of milk.