diff --git a/week12/inClass_week12.ipynb b/week12/inClass_week12.ipynb
index d383cda..d5bc222 100644
--- a/week12/inClass_week12.ipynb
+++ b/week12/inClass_week12.ipynb
@@ -286,7 +286,7 @@
   {
    "cell_type": "code",
    "execution_count": 7,
-   "id": "bf5ecd7c",
+   "id": "fd9fabb0",
    "metadata": {},
    "outputs": [
     {
@@ -306,10 +306,20 @@
     "plt.show()"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "id": "2672af05",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "buildings.loc[buildings['Year Acquired']==0,'Year Acquired'] = np.nan"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "88595af8",
+   "id": "4a9e4648",
    "metadata": {},
    "outputs": [],
    "source": []