diff --git a/optimization/exercises/singVarCalcOptimization13.tex b/optimization/exercises/singVarCalcOptimization13.tex
index 7a0a3a6b5..5e7f7de5a 100644
--- a/optimization/exercises/singVarCalcOptimization13.tex
+++ b/optimization/exercises/singVarCalcOptimization13.tex
@@ -75,7 +75,7 @@
                                 
                                 $A\left(\frac{10}{2+\pi}\right)=\frac{50\pi}{(2+\pi)^2}$
                                 
-                                $A\left(\frac{\answer{10}}{4+\pi}\right)=\frac{\answer{50}}{4+\pi}\approx 7$
+                                $A\left(\frac{\answer{10}}{4+\pi}\right)=\frac{\answer{200+350\pi}}{(4+\pi)^2}\approx 7$
                                 
                                 This seems complicated. It is better to argue that the derivative