The length of a rectangle is 3 meters less than twice it’s width.

l=2w-3

Explaniation

1) Let  

w

represent the width of the rectangle.

2) "Twice its width" is the same as multiplying by  

2

which would give  

2

w

3) "3 meters less than" means to subtract  

3

or "- 3".

4) combining these would give the equation for the length, lets call it  

l

, as:

l =2w-3