Answer
The velocity of the glider just after the skydiver lets go is still 30 m/s
Work Step by Step
Let $m_g$ be the mass of the glider after the skydiver lets go. Let $m_s$ be the mass of the skydiver. We can use conservation of momentum to find the velocity $v_{fx}$ of the glider after the skydiver lets go. Note that after the skydiver lets go of the glider, the skydiver still has a horizontal velocity of 30 m/s.
Let's consider the system of the glider and the skydiver;
$p_{fx} = p_{0x}$
$m_g~v_{fx}+m_s~(30~m/s) = (m_g+m_s)~(30~m/s)$
$m_g~v_{fx} = (m_g)~(30~m/s)$
$v_{fx} = 30~m/s$
The velocity of the glider just after the skydiver lets go is still 30 m/s.
