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A Mechanics Question About Resolving Forces

Hey, I'm trying to do some revision for my Mechanics which is actually so confusing at the moment. I've been working at this question for quite a while but I keep on getting stuck because I do not really know how we're meant to go about doing it.

The question is this:

A sack of weight 600N is being loaded onto a truck up a ramp inclined at 18 degrees to the horizontal. A rope attached to the sack is held at an angle of 25 degrees to the ramp. The coefficient of friction between the sack and the ramp is 0.3. What tension in the rope is needed

a) to prevent the sack from sliding down the ramp,
b) to pull the sack up the ramp at a steady speed?

Any pointers will be appreciated. Supposedly there is something to do with static friction? But I cannot figure out what is actually happeneding there. =S

Thank you in advance!