To construct triangle PST with angle PST = 30°, ST = 9 cm, and PS = 12 cm using a ruler and a pair of compasses only, follow these steps:
Draw a line segment PS of length 12 cm using a ruler.
From point P, draw an arc with radius 9 cm using a compass.
From point S, draw another arc with radius 12 cm using a compass.
The two arcs should intersect at point T.
Draw a line segment from point T to point P to complete the triangle PST.
The resulting triangle should have angle PST = 30°, ST = 9 cm, and PS = 12 cm