Answer:
So mass of the object will be 3.2 kg
Explanation:
We have net force on the object F = 16 N
Acceleration of the object 
We have top find the mass of the object
From newton law of motion we know that force is given by
F = ma , here m is mass and a is acceleration
So 

So mass of the object will be 3.2 kg
when you solve an equation the quadratic of g(f) must be treated like any other mathematical quantity— they must be multiplied, divided, raised to powers, cancelled, etc in exactly the same way as the numbers to which they belong
I would use miles
Because miles will give you less of an answer