Using Newton's law that F = ma.
The force here is the net force. The forces acting in opposite direction are the weight and the air resistance. The weight of course is acting downwards and the air resistance is pushing upwards.
Therefore:
W - AR = ma W = Weight = mg, AR = Air Resistance = 150.
g = 10 m/s2
mg - AR = ma
60(10) - 150 = 60a
600 - 150 = 60a
450 = 60a
60a = 450
a = 450/60
a = 7.5 m/s2
Cheers.
