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