Seems correct - they want you to plot the point (20, sin(20)), which is indeed (20, 0.342).
Confirming ebaines' reply.
Hint to what you might want to notice: Once you're finished the graph, look where points are at the same height (amplitude, y-value, sin(theta) value) and the difference in theta between them! If what I said is complicating, then please ignore this.