Let Xg, the salt water, be poured out for the first time, leaving 60-X g of salt water, and then add 1X/3 g of water. At this time, the salt content of brine is (60-X)*20% g, and the total quality of brine is (60+2X/3)g, which can be listed.

Equation ((60-x) * 20%)/(60-2x/3) =15%.

Solve this equation to get X=30g, that is, pour out 30g of brine.