Answer
$v=12\frac{m}{s}$
Work Step by Step
We know that the speed $v,$ tension $T$ and linear density $\mu$ are linked by the equation:
$v=\sqrt\frac{T}{\mu}$
We plug in the known values to obtain:
$v=\sqrt\frac{3.6}{25\times 10^{-3}}$
$v=12\frac{m}{s}$
