In order to determine if there is a positive change or negative change in the water volume of the lake, proceed as follow:
Convert 258,000 cubic feet to gallons:
Now, consider as positive values the volume of water in the lake and the annual volume of precipitation, and as a negative value the annual colume of evaporation.
Then, you can write for the change in the total volume of water:
change = 1,929,840gal - 1,800,000gal
change = 129,840gal
Hence, the change in the volume of the water in the lake is positive