The length is given to be L, and width is given to be W.
The Perimeter, P of a rectangle is given as:

It is given that P=86, substitute this into the equation:

It is also given that the length is 1cm more than twice its width, it follows that:

This gives the equation for L in terms of W.
Substitute this into the first equation:

Solve the equation for W:

The width is 14 cm.
Substitute the value of the width into the equation for L:

Answers:
The equation for P in terms of L and W is: P=2L+2W
The equation for L in terms of W is: L=2W+1
The length is 29 cm and the width is 14 cm.