yes what Tartan said.
A word of caution though. All three of your triangles have bias edges. You will be sewing two bias edges together - the two edges of the green triangle to each edge of the rose and cream triangle.
Bias edges STRETCH.
You can do a few things to stabilize those edges.
Heavy starch (and I do mean HEAVY and STIFF)
Paper or some other tear away stabilizer.
Because the pieces are already cut I would opt for a paper stabilizer. If you were to starch them now and iron them I could almost guarantee they will skew under the dampness from the starch and the iron.