Maths problem: how to do, thanks?

(a)
Number of passengers on tram
= 50 × (1 - 3/5) + 4= 50 × 2/5 + 4
= 20 + 4
= 24

(b)
Number of passengers on tram
= 24 × (1 - 1/4) + y
= 24 × 3/4 + y
= 18 + y

(c)
Number of passengers on tram
= (18 + y) × (1 - 1/3) + 5
= (18 + y) × 2/3 + 5
This number is half of 50 = 0.5 × 50 = 25
Therefore,
(18 + y) × 2/3 + 5 = 25
(18 + y) × 2/3 = 20
18 + y = 20 × 3/2
18 + y = 30
y = 12