Mohon bantuannya ya buat no. 19

vB / vX = √(2G MB / RB) / √(2G MX / RX)
vB / vX = √[MB RX / (MX RB)]
vx = vB √[MX RB / (MB RX)]
     = v √[16MB RB / (MB 9RB)]
     = 4/3 v