Further Mechanics Question Edexcel

A block of mass 2kg rests on a rough plane which is inclined at 30 degrees to the horizontal. The block is attached to a point at the top of the plane by means of an elastic string of natural length 2m and modulus of elasticity 100N. The coefficient of friction between the block and the plane is 0.25. Calculate the distance between the lowest and highest positions in which the block will rest in equilibrium.

What have you tried, have you drawn the forces diagram?
Note, that friction opposes motion so will be in the opposite direction at the two different positions.

Basically I've got two different equations for going up and going down, but they're not giving me the right answer so I'm not sure where I've gone wrong.

UP: $\frac{\lambda(k+2)}{L} - {\mu}R - mgsin(30)$

DOWN: $mgsin(30) - \frac{\lambda(k+2)}{L} - {\mu}R$

These give a difference of 0.196m for k - but the book says the answer is 0.170m.