Oh, bingo! Light goes on! Thanks to OBJ......
In your flight plan example, the aircraft is planning to fly at 155 knots("N0155") and changing altitudes during the flight, descending from 7000ft (A70) down to 4000 feet (A040).
I borrowed this text from this site, http://www.skybrary.aero/index.php/Flight_Plan_Filling
( I have no idea who owns it)
(A) Cruising Speed (maximum 5 characters)
Insert the true airspeed for the first or the whole cruising portion of the flight, in terms of:
a) kilometres per hour expressed as “K” followed by 4 figures
Example: K0220 (which means 220 km/h true airspeed)
b) knots expressed as “N” followed by 4 figures
Example: N0175 (which means 175 knots true airspeed)
There is also an option to indicate speed as Mach number but as it is not used by GA no details will be provided.
General aviation example: N0150 (assuming that You will fly with speed 150 knots)
(B) Cruising Level (maximum 5 characters)
Insert the planned cruising level for the first or the whole portion of the route to be flown, in terms of:
a) flight level, expressed as “F” followed by 3 figures or
Example: F085 (which means flight level 085),
b) standard metric level in tens of metres, expressed as “S” followed by 4 figures
Example: S0150 (which means 1500 metres)
c) altitude in hundreds of feet, expressed as “A” followed by 3 figures
Example: A055 (which means 5500 feet altitude)
d) altitude in tens of metres expressed as “M” followed by 4 figures
Example: M0610 (which means 6100 metres altitude)