For the first figure ~
The diagonals of a kite intersect each other at 90°
So, we can apply Pythagoras theorem here :
For the second figure ;
we have same concept of kite, and use of Pythagoras theorem !
Also, the diagonal QS bisects diagonal PR
Hence,
now, apply pythagoras theorem ~
here, 2 OR = 2 OP = PR
so, similarly OP = 5 mm
Applying pythagoras theorem again ;