If you would like to know how much water did Elena drink each practice if she drank the same amount each time, you can calculate this using the following steps:
5 bottles of water ... 7 practices
x bottles of water = ? ... 1 practice
5 * 1 = 7 * x
5 = 7 * x /7
x = 5/7 bottle of water
The correct result would be 5/7 bottle of water.