Tolong jawab no sempat ya please

4 jam 30 menit = 4 1/2 jam = 9/2 jam
4 jam 30 menit + 15 menit = 4 jam 45 menit = 4 3/4 jam = 19/4 jam

100/400 = 1/4
1 - 1/4 = 3/4

Kereta = k
Mobil = m

1/2 k + 1/2 m = 9/2
Dikalikan 2
k + m = 9......(1)

1/4 k + 3/4 m = 19/4
Dikalikan 4
k + 3m = 19......(2)
k + m = 9
------------------ -
2m = 10
m = 10/2 = 5 jam

k + m = 9
k + 5 = 9
k = 9 - 5 = 4 jam

Maka, 
Kecepatan mobil = 400/5
Kecepatan mobil = 80 km/jam

Kecepatan kereta = 400/4
Kecepatan kereta = 100 km/jam

Semoga membantu...
Mohon maaf apabila kurang tepat...