Can someone help me with these, please

1. The length of a rectangle is 6cm less than twice its width. Find the dimensions of a rectangle if its area is 108cm^2 (squared)?

2. Find the dimensions of a rectangle whose perimeter is 46m and whose area is 126m^2 (squared).

3. Find the dimensions of a rectangle whose perimeter is 42m and whose area is 104^2 (squared).

Please help

EDIT: Please help, I don't understand it at all. Our teacher always starts a new chapter on the day of the previous test and between periods we don't get anytime to comprehend much.