$f_1: f_2: f_3=1: 2: 3$
$\Rightarrow \frac{1}{L_1}: \frac{1}{L_2}: \frac{1}{L_3}=1: 2: 3$
$\Rightarrow L_1: L_2: L_3=\frac{1}{1}: \frac{1}{2}: \frac{1}{3}$
$\Rightarrow L_1: L_2: L_3=6: 3: 2$
Let $L_1=6 x, L_2=3 x, L_3=2 x$
Total length of sonometer wire $=110 cm$
$L_1+L_2+L_3=110$
$6 x+3 x+2 x=110$ $x=10$
$\therefore L _1=60 cm , L _2=30 cm , L _3=20 cm$
Hence, bridges should be placed at distance of $60 cm$ and $90 cm$ from $A$.
$y(x,t)\, = \,0.6\,\sin \,\left( {\frac{{2\pi }}{3}x} \right)\,\cos \,(120\,\pi t)$
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 .... $N$