Hey there! I'm happy to help!
First, let's find out how much water evaporated. We have 175 left of the 250 after evaporation, so we need to subtract 175 from 250 to see how much water evaporated.
250-175=75
75 liters evaporated. Now, we want to find this as a percent out of 250. 75 is what percent of 250? Well, when talking about percents, the word "is" means "equals". So, we can turn this into an equation! We will use x to represent our percent as a decimal.
75= x·250
We simply divide both sides by 250 to isolate the x, giving us x=0.3
0.3 is 30% as a percent, so this means that 30% of the water evaporated.
I hope that this helps! Have a wonderful day!