Answer
$d = 24~cm$
Work Step by Step
We can find the wavelength:
$\lambda = \frac{v}{f}$
$\lambda = \frac{340~m/s}{10,000~Hz}$
$\lambda = 3.4\times 10^{-2}~m$
We can find the spacing between the slits:
$y = \frac{\lambda~L}{d}$
$d = \frac{\lambda~L}{y}$
$d = \frac{(3.4\times 10^{-2}~m)(10~m)}{1.4~m}$
$d = 0.24~m$
$d = 24~cm$
