For this question the answer is 2.5m (B)
You find this by: L=0.85m
W=0.4m
A rectangle had 4 sides (2 lengths and 2 widths)
So...
To find 1 length and 1 Width you do 0.85+0.4=1.25m
Now you want to find the other 2 sides (L and W)
You can do: the same method and add it to 1.25m OR...
You can do (I prefer this one): (0.85+0.4)x2=?
This is the same as 0.85+0.4=1.25
1.25x2=2.5m