A lot of values are given but we must focus only on HCl.
There are 215 mL (0.215 L) of 0.300 M HCl that was completely used. We must remember the moles is simply the product of volume and molarity, that is:
number of moles = 0.215 L * 0.300 M
number of moles= 0.0645 moles HCl