${z_1} = a\cos (kx - \omega \,t)$.....$(A)$
${z_2} = a\cos (kx + \omega \,t)$.....$(B)$
${z_3} = a\cos (ky - \omega \,t)$..... $(C)$
$y(x,t)\, = \,0.6\,\sin \,\left( {\frac{{2\pi }}{3}x} \right)\,\cos \,(120\,\pi t)$
where $x$ and $y$ are in $metre$ and $t$ in $second$ . The length of the string is $1.5\,m$ and its mass is $3.0\times 10^{-2}\,kg$ the tension in the string will be .... $N$