All the sides of a rhombus are equal.
So, PQ=QR=7.5 cm
A rhombus is also a parallelogram so,
∠QPS=∠SRQ=75o
(opposite angles of a parallelogram are congruent)
Also, ∠QPS+∠PQR=180o
(interior angles on the same side of the transversal are supplementary)
⇒75o +∠PQR=180o
⇒∠PQR=105o