Power of String Oscillation

Classical Mechanics

A piece of string of linear mass density $20 \文本{g} /{厘米}\文本$ oscillating with amplitude $2 \text{ cm}$ 和频率 $50 \text{ Hz}$ carries an energy of $12 \text{ J}$ per wavelength of oscillation. What is this wavelength in meters?

1.2

0.7

0.3

0.02