Solution :
It is given that force on the object is directly proportional to acceleration.
So, F = ka
Here, k is any constant value.
Putting, F = 27 N and a = 3 m/s² in above equation, we get :
3k = 27
k = 9 N s² m⁻¹
Putting, k in above equation, we get :
F = 9a
Now, putting F = 18 N, we get :
a = 18/9 m/s²
a = 2 m/s²
Hence, this is the required solution.