To develop this problem it is necessary to apply the concepts related to Wavelength, The relationship between speed, voltage and linear density as well as frequency. By definition the speed as a function of the tension and the linear density is given by

Where,

T = Tension

Linear density

Our data are given by

Tension , T = 70 N

Linear density ,

Amplitude , A = 7 cm = 0.07 m

Period , t = 0.35 s

Replacing our values,

Speed can also be expressed as

Re-arrange to find \lambda

Where,

f = Frequency,

Which is also described in function of the Period as,

Therefore replacing to find

Therefore the wavelength of the waves created in the string is 3.49m