Question 278773
Here's a hint. Instead of focusing on the percentage of quarts, focus on the total percentage.

So as you noted, after adding the water at the end of the first week, there will again be 16 quarts in the radiator. But now, instead of 50% being anitfreeze, only 7/16 or 43.75% is antifreeze.

Now let another week go by and two more quarts leak out. Now there are 14 quarts left in the radiator -- with a density of 43.75% antifreeze.

So 14*0.4375 = 6.125 quarts of antifreeze are left.

Add two more quarts of water and do the same type logic above.
Etc
Hope that helps