Answer: 15 Liters (15L)
Explanation:
The constant of proportionality (also known as k), is for every bottle, there are 2.5 liters. (k = y/x)
5 / 2 = 2.5 , 12.5 / 5 = 2.5, 20 / 8 = 2.5, etc.
So, we need to multiply 6 by 2.5, 6 * 2.5 = 15
For 6 bottles, there are 15 liters