Answer:
10kg
Step-by-step explanation:
The information we have is: 
Force: 

acceleration: 

What we need to know is the mass of the object. For this we can use Newton's second law:

Where F is the Force applied, m is the mass of the object, and a is its acceleration.
from this equation we clear for the mass 
 :
:

and we substitute the known values: 

The mass of the object is 10kg