Chapter 31 - Atomic Physics - Problems and Conceptual Exercises - Page 1114: 62

$\Delta E=66.9KeV=1.07\times 10^{-14}J$

We know that $\Delta E=E_K-E_L$ $\implies \Delta E=\frac{-13.6(Z-1)^2}{(1)^2}-\frac{-13.6(Z-1)^2}{(2)^2}$ This simplifies to: $\Delta E=66.9KeV$ $\implies \Delta E=1.07\times 10^{-14}J$