Dan is gliding on his skateboard at 4.00 m/s . He suddenly j…

Dan is gliding on his skateboard at 4.00 m/s . He suddenly jumps backward off the skateboard, kicking the skateboard forward at 8.00 m/s . Dan’s mass is 70.0 kg and the skateboard’s mass is 6.00 kg .  How fast is Dan going as his feet hit the ground?