VHF Omni-directional Range: DGCA Air Navigation questions

Assuming the maximum likely error in VOR to be 5.5 degrees, what is the maximum distance apart that beacons can be situated on the centre line of a UK airway in order that an aircraft can guarantee remaining within the airway boundary?

The Designated Operational Coverage quoted for VOR beacons in the COMM section of the AIP:

An aircraft is tracking away from a VOR on the 050 radial with 10 degrees starboard drift. An NDB lies to the east of the VOR. Which of the RMIs illustrated below shows the aircraft when it is obtaining a relative bearing of 100 degrees from the NDB?

What is the theoretical maximum range that an aircraft at flight level 360 will obtain from a VOR beacon situated at 900 ft above mean sea level?

A conventional VOR: