Consider that the object experiences two forces at time: gravitational force (which is the weight of the object) and friction force due to air resistance. The net force over the object id then:
F = W - Fr
where,
F: net force
W: weight
Fr: friction force = 100.0N
The net force is equal, by Newton second law, to F = m*a, where m is the mass of the object and a is the acceleration.
Then, you have:
m*a = W - Fr
a = (W - Fr)/m
Consider that the weight of the object is:
W = m*g = (17.0 kg)(9.8 m/s^2) = 166.6 N
Then, by replacing the values of W, Fr and m into the expression for a, you obtain:
a = (166.6N - 100.0N)/(17.0kg)
a = 66.6N/17.0kg
a = 3.9 m/s^2
Hence, the acceleration of the object is approximately 3.9 m/s^2