Step 1: Analyze forces.
The block is pulled at constant speed, so net force along the plane is zero. Tension \(T\) balances the component of weight along the incline:
\[
T = mg \sin \theta
\]
Step 2: Substitute values.
\[
T = 2 \times 10 \times \sin 30^\circ = 20 \times 0.5 = 10 \, \text{N}
\]
Step 3: Calculate work done.
Work done by the tension along the plane over distance \(d = 4 \, \text{m}\) is:
\[
W = T \cdot d = 10 \times 4 = 40 \, \text{J}
\]
Step 4: Verify reasoning.
Since the plane is frictionless and motion is at constant speed, no extra work is done; all work goes into counteracting the component of gravity.
Step 5: Final conclusion.
Hence, the work done by the tension in the rope is:
\[
\boxed{40 \, \text{J}}
\]