The motion of the packet is a uniformly accelerated motion, with constant acceleration a=g=9.8 m/s^2 directed downward, initial vertical position d=750 m, and initial vertical velocity v_0 = 0

so what do you want?

a = -9.8
v = Vi - 9.8 t = 0 - 9.8 t because initial velocity Vi = 0
height = d = 50 + Vi t - (9.8/2) t^2
or
d = 50 - 4.9 t^2