Simply add the different container sizes together. The first container holds x - 10 liters, the second holds x - 5 liters, and the third holds x liters.
(x - 10) + (x - 5) + x
Because of the associative property of Addition, we can remove the parentheses.
x - 10 + x - 5 + x
Because of the communicative property of addition, we can reorder the terms so that the like terms are next to each other.
