Answer:
f=156Hz
F=467.25N
wavelength =1.6m
Step-by-step explanation:
we have two frequencies from the question 624hz and 780hz.
let them be f1 and f2
f1=624=nv/2L
f2=780=(n+1)v/2L

624n+624=780n
n=4
velocity=2f1l/4
v=624*0.8/2
V=249.6m/s
The fundamental frequency of a wave is the following
f=v/2L
f=249.6/1.6
f=156hz
v=

T=v^2u
=249.6^2*7.5*10^-3
T=467.25N
f=156Hz
T=467.25N
T=tension in the string
wavelength is
v=f w
w=249.6/156
w=1.6m