diff --git a/_psets/5.md b/_psets/5.md
index a5aa5c092f4cfd57a4530fde4c716ed771eef31d..d3a8df09558b13c973bc1569e5a3d2cd981c6dad 100644
--- a/_psets/5.md
+++ b/_psets/5.md
@@ -28,6 +28,14 @@ to go, though not all shields are grounded.
 
 Salt water has a conductivity ∼4 S/m. What is the skin depth at $$10^4$$ Hz?
 
+$$
+\begin{align*}
+\delta &= \frac{1}{\sqrt{\pi \nu \mu \sigma}} \\
+&= \frac{1}{\sqrt{\pi \cdot 10^4 \si{Hz} \cdot \num{1.3e-6} \si{H/m} \cdot 4 \si{S/m}}} \\
+&= 2.5 \si{m}
+\end{align*}
+$$
+
 ## (7.3)
 
 Integrate Poynting’s vector $$P = E \times H$$ to find the power flowing across a cross-sectional