Correct equation display error

chapters/project/FinalProject-2023Fall.ipynb

@@ -256,7 +256,7 @@
     "### Appendix\n",
     "Exposure to heat extremes is associated with premature death. Assume the empirical relationship between temperature and excess mortality rate for the 45- to 64-year-old population can be estimated by:\n",
     "\n",
-    "$\n",
+    "$$\n",
     "\\text{Mortality}=  \n",
     "\\begin{cases}\n",
     "-0.54 * T - 0.2,  T \\le -10\\\\\n",
@@ -265,7 +265,7 @@
     "0.5 * T - 12.65, 22 < T \\le 25 \\\\\n",
     "0.75 * T - 18.9, T > 25 \\\\\n",
     "\\end{cases} \n",
-    "$\n",
+    "$$\n",
     "\n",
     "where $\\text{Mortality}$ is the excess mortality (per 100k) for the 45- to 64-year-old population and $T$ is the temperature (°C). \n"
    ]