Need help pls. Thank u

Without loss of generality, say Benny has $120.

He just spent 24 dollars on 4 pineapples and 8 mangoes.

Since a pineapple is 4 times a mango, Benny spent 1 dollar per mango and 4 dollars per pineapple. 

He now has 96 dollars, and he spends $48 on pineapples, accounting for 12 pineapples. 

He has bought 12+4 = 16 pineapples.

x = original money amount

 

p = 4m      (given)

   or   1/4 p = m

1/5 x  =  4p + 8 ( 1/4 p)

1/5 x = 6p

 

he has 4/5 of his money left     he spends 1/2 of this   or  4/10 x

 

ratio     (1/5 x) / (4/10 x) = 6p / ?

              10/20 = 6p / ?

                ? = 12        plus the original 4   = 16 pineapples