Problem involving Tension and Friction on a slope

Any help with the following question would be greatly appreciated.

Q: Alan pulls a container with weight of magnitude *W* newtons at a constant speed up a rough plane, with coefficient of friction , inclined at an acute angle to the horizontal by means of a light inextensible rope. The rope also makes an angle of to the inclined plane.

(a) Show that the magnitude of the tension of the rope is given by

newtons.

(b) Determine the range of values of for which the tension in the rope is less than the weight of the container.

(Although it is not stated in the question it is clear that or the string would be vertical.

Attempt:

Resolving Parallel to the plane:

Resolving Perpendicular to the plane:

Squaring and adding gives

And I'm a bit stuck now - I seem to be a long way from the target answer