Question 495605
Let x=amount of water that needs to be boiled off

Now we know that the total amount of salt that exists before before x amount of water is boiled off has to equal the total amount of salt that exists after the water is boiled off.

Total amount of salt before the water is boiled off is (2 liters)*90 g/l=180g
Total amount of salt after x amount of water is boiled off is (2-x)liters*180g/l
Soooo
180g=(2-x)180g/l
180=360-180x
-180x=-180
x=1 liter

Hope this helps ---ptaylor