What would be the pH if one drop $(0\mathrm{.}5$ mL$)$ of $1\mathrm{.}0$ M HCL was added to $0\mathrm{.}25$ L of H$2$O that contains $50$mM acetic acid and $75$mM of sodium acetate. The pKa of acetic acid is $4\mathrm{.}76.$ Please show your work.