Answer:
The vase had 1 milliliter of water at the very beginning
Explanation:
Equations
Suppose there were x milliliters of water in the vase. Ava added 35 milliliters of water to the vase. Now the vase has x+35 milliliters of water. Now Ava poured out 10 milliliters, the vase has x+35-10 milliliters. That is equal to 26:

Solving for x

The vase had 1 milliliter of water at the very beginning
Note we could have solved the problem without the aid of an equation, just adding the quantity poured out and subtracting the quantity first added to the final contents of the vase