A package of weather instruments is propelled into the air to a certain altitude at which point a parachute opens and the package returns to the surface. The altitude y (in km) of the package as a function of the time t (in min) is given by

. Find the vertical velocity of the package for

min.
◦
-0.85 km/min
◦
-0.98 km/min
◦
-0.74 km/min
◦
-0.68 km/min