Hi,

after 15 quarts of water evaporated, there are 60 - 15 = 45 quarts of water left.
New volume of water compare to the original one: 45/60 = 3/4

The concentration is calculated as = amount of salt / amount of water

As salt did not evaporate as water did. Then the amount of salt remains unchanged.

New concentration = original amount of salt / new amount of water
= original amount of salt / (3/4* original amount of water)
= 4/3* (original amount of salt/ original amount of water)
=4/3 * original concentration
= 4/3* 3% = 4%

Hence pick B.

My IQ is way lower so I solved it this way...

3% of 60 = 1.8 salt
thus 60 - 1.8 = 58.2 water
1.8salt + 58.2 water = 60

If we remove 15 water:
1.8 salt + 58.2 water - 15 water = 60 - 15
1.8 salt + 43.2 water = 45

Now we need to find the % of salt:
1.8/45 = 18/450 = 6/150 = 1/25

Let see if we can change the denominator to 100:
1/25 * (4/4) = 4/100 = 4%

Correct Answer (B)