Hi there!
On the object, we know that there are two forces working on the object:
-Force due to gravity (Mg)
-Force due to air resistance
Let the positive direction of the force be downwards (direction of the acceleration)
We can write the summation of forces as:
∑F = Mg - Fa
Plug in values. Let g ≈ 10 m/s²
∑F = 30(10) - 50 = 250N
Find the acceleration using the formula:
∑F = m · a
∑F/m = a
Plug in values:
250/30 = 8.33 m/s²