I'm assuming it is -m, +m, -m, +m etc..
Answer:
10 you just add them and or count down
Set up a pair of fractions:

500x = 828 (cross multiply)
x = 1.656 meters high should be the model (1.7 rounded)
N
- -11 = 3
2
wouldn't n=26? because 26 divided by 2 is 13 then subtract 11 and you get 3