A drone flies horizontally due east at 5 m/s while simultaneously ascending at 3 m/s. At the instant the drone is 12 m east of its take-off point and 16 m above the ground, what is the rate of change of its straight-line distance from the take-off point?
a) 8.0 m/s
b) 5.8 m/s
c) 5.4 m/s
d) 4.8 m/s