Force of 99N and 64N act on an object of mass27 kg. what is the acceleration of the object

That all depends on the angle between the two forces.

It could be anything between 1.3 m/s² in the direction of the larger force, if

they're in opposite directions, all the way around to 6.04 m/s² in the direction

of both of them if they're both in the same direction.

That includes magnitudes between 1.3n and 6.04n directed somewhere between

the two forces if they're in different, unrelated directions.