Distance between wall and D is 8 cm \ \

Distance between wall and P is 20 cm \ \

From the above geometry

Distance between P and D is 20-8=12 cm

P is the midpoint,therefore AP=PD=x=12 cm

Distance between wall and A is 20+x

Substitute 12 cm for x in above

20+x=20+12=32 cm

32 cm far A is from the wall

I hope that helps u