Step-by-step explanation:
There are two forces acting on the object in opposite directions.
The sketch of the two forces is
since the force acting towards the left is greater than the force acting on the right, the object will accelerate towards the left.
Now, how much force is required to counter 25 N acting on the left?
The answer is, if we apply an additional 15 N towards the right, the total force acting in this direction is 10 + 15 = 25 N, which is enough to counter 25 N acting towards the left.
Therefore, we need to apply an additional 15 N in the direction of the 10 N force.