Arectangular garden has a perimeter of 54 feet. it's length is 3 less than twice its width. write and solve an equation to solve for the gardens dimensions

2(L+W)=54
L=2W-3
Substitute L in the first equation:
2((2W-3)+W)=54. 
Divide by 2:
(2W-3)+W=27
Simplify by collecting like terms:
3W-3=27. 
Add 3:
3W=30.
Divide by 3 to get that 
W=10. 
Substitute the L and W relations to get 
L=2W-3
L=2*10-3
L=17. 
The answers are length is 17 and width is 10.