I believe it has something to do with the H2O molecules, because a chemical compound is not a mixture.
Answer : The volume of water added are, 15 mL
Explanation :
Formula used :

where,
are the initial molarity and volume of HCl.
are the final molarity and volume of water.
We are given:

Putting values in above equation, we get:

Hence, the volume of water added are, 15 mL
Tell the teacher, do NOT clean it up yourself.
Answer:
A bohr developed a model of atom that predicts how it will behave.