Weird autopilot question
This question includes a chart. Info might be needed is:
Straight in ILS min for cat C is 271(204) and vis of 1200m.
Rwy 33R threshold elevation is 67'
Airport elevation is 68'
You are performing an ils approach to runway 33R. (CAT C aircraft). Using your autopilot couples to the ILS, you receive the following MET data: Visibility: 8000m, BKN 2000". The maximum altitude loss for a malfunction of the autopilot under approach conditions is 40'. What is the lowest altitude at which you can use the autopilot.
I am totally lost about this one.
The answer they provide is 118ft.