I don't understand

Let say papaya = 5u
So, Pineapple = 393 - 5u

After sold 80% of papaya. Left 20%
= 5u × 20/100
= 1u
a) Faction of papaya left = 1u/5u = ⅕

After sold Pineapple 43,
left = 393 - 5u - 43
= 350 - 5u ↣(2u)
2u = 350 - 5u
7u = 350
1u = 50
b) Fruit left
Papaya = 1u
Pineapple = 2u
Total = 3u = 3 × 50 = 150.

U might ask why papaya at 1st = 5u

Cause after sold 80%, left 20% given is 1u
20%↣1u
100%↣ 5u (at 1st).

Thanks for the clear explanation.