From Mechanics

Resolving vertically upwards,

\displaystyle T\cos {{30}^{\circ }}+S-mg=0

where \displaystyle S is the spring force which we assume is upwards.

This gives

\displaystyle S=mg-\ T\cos {{30}^{\circ }}=40\times 9\textrm{.}8-90\times 0\textrm{.}866=314\ \text{N}

As \displaystyle S is positive this means the spring is pushing upwards on the mass and thus the spring is in compression. (If \displaystyle S had been negative the spring would have been pulling downwards on the mass and thus would be in tension).