tolong bantuin dong, secepatnya hehe

S = 10 km = 10^4 m
c = 3.10^8 m/s
S = c.t/2
10^4 = (3.10^8 × t)/2
2.10^4 = 3.10^8 t
t = 2.10^4/3.10^8
t = 6,67×10^-5 dtk