so

we know that triangle APQ is an equilateral triangle because it has a 60 degrees angle.

a)which means that PQ=AP=AQ=2cm.

b)you can use congreunce of triangles PDC and CBQ. where you have 2 equal lines DP and QB

BC=DC

and 2 equal opposite angles in the rhombus.

then you got b)PC=QC

c) looking at triangle QBC:

QB=60-2=58

BC=60

angle B=120

then you get QC with the cosine rule.

then you use the cosine rule in triangle PQC