\textbf{191.} A string fixed at both ends has a length of 40 cm and its fundamental frequency is 150 Hz. If the mass per unit length of the string is 20 milligrams per centimeter, what is the tension in the string in newtons?
$$
(1)\quad 14.4 \qquad (2)\quad 28.8 \qquad (3)\quad 144 \qquad (4)\quad 288
$$
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