Explanation:

52

Average age = 32

Sum 0f ages of 4 people=  average age* 4

                                       =32*4

                                       =128

Increased in average age=  32* (112.5/100)

                                        =  32 (9/8)

                                        = 36

average age of 5 people( including guest)=  ( ages of 4 people  + age of guest)/5

36*5   =    (128 +x)

X=180-128

X= 52