Mohon Bantuanya .tolong bantu saya

f = n/t
  = 6 / 1,5
  = 60 / 15
  = 4 Hz

T = 1 / f
    = 1 / 4
    = 0,25 s 

v = lamda x f
   = s/n x 4
   = 90 / 3 x 4
   = 30 x 4
   = 120 cm/s

Jawabannya A

Semoga membantu..^^

Dik: Σ getaran/n = 6
t = 1,5s
s = 180cm

f = n / t
= 6 / 1,5
= 4 Hz
T = 1/f
= 1/4
v = s / t
= 180 / 1.5
= 120cm/s