tolong bantu jawab dong please buat bsk pr di kumpulin

Dik :
v = 10 cm /s
n = 2,5
lamda = 40
Dit :
f = .......?
Jawab :
lamda = 40/2,5
= 16
v = lamda × f
10 = 16 × f
10/16 = f
0,625 = f