Radius of one steel ball bearing

$r = 6 \, \text{ mm} = 0.006 \, \text{ m}$

Volume of 100 000 steel ball bearings

$V = 100\,000 [ \, \frac{4}{3}\pi(0.006^3) \, ]$

$V = 0.0288\pi \, \text{ m}^3$

Weight of 100 000 steel balls bearings

$W = \gamma V = 75.5(0.0288\pi)$

$W = 6.8311 \, \text{ kN}$ *answer*