Suppose you have 5 apples and I have 2 apples less than you. So how do you solve this ? Clearly I have less apples than what you have. You will subtract 2 from 5 i.e. 5-2 = 3 apples. However, if you subtract 5 from 2 i.e. 2-5 = -3, the result will be in negative.
Width is 8 feet less than twice the length,
It states that width is 8 unit less than 2L (twice the length).
So, the width "w" will be
w=2L-8
Also, not length is always greater than width.
In example 1 you can write either way because it's simply addition (1+2) = (2+1), order doesn't matter:
3W+1 is same as 1+3W
But in subtraction order change will result in sign reversal.