This page is an exercise in using Hess' Law. When you press "New Problem" a reaction set with a single missing enthalpy will be displayed. Calculate the needed enthalpy, enter it in the cell and press the "Check Answer"
button. The results will appear in the table. There should be a straightforward combination of the contributing reactions which yields the desired reaction. Pressing "Show Answer" will cause the correct answer to appear and you will no longer be able to submit an answer for that problem.