All the sides of a rhombus are equal.

So, PQ=QR=7.5 cm

A rhombus is also a parallelogram so,

∠QPS=∠SRQ=75^{o}

(opposite angles of a parallelogram are congruent)

Also, ∠QPS+∠PQR=180^{o}

(interior angles on the same side of the transversal are supplementary)

⇒75^{o} +∠PQR=180^{o}

⇒∠PQR=105^{o}