You need to start with solving for the unit vector along each of the three legs (find the i, j, and k components and then divide by the magnitude of the components)
Then you can muliply the compressions by their unit vectors
You should then be able to set up three different equations
Σ Fx = 0
Σ Fy = 0
Σ Fz = 0
Out of these three equations you should now have values for the compressions in each of the legs