tolong ya nomor 6... thx

3λ = 400 m
λ = 400/3 m

v = f.λ = 30 × 400/3 = 4.000 m/s
T = 1/f = 1/30 dtk (A)

C
400cm = 4m
Lamda = x/n
= 4/3
V = lamda*f
= 4/3*30 = 40 m/s
T = 1/f = 1/30