Suppose each person applies a force F to push the motorcar.

So, Total force applied by two persons=F+ F

=2F ....(1)

Since this force (2F) gives a uniform velocity to the motorcar along a level road (where work is done only against the force of friction), so the force 2F can be taken as being equal to the force of friction f between the motorcar and the road. That is,

Force of friction, f=2F ....(2)

Now, when three persons apply force to push the motorcar, then:

Total force applied by three persons=F+ F+F

=3F .....(3)

Now, the total force applied by three persons is 3F whereas the opposing force of friction is f. So,

Force that produces acceleration=3F-2F ...(4)

But from equation (2), we have f=2F.So,

Force that produces acceleration=3F-2F

or Force that produces acceleration=F

Now, Force =mass `xx` acceleration

F=m`xx`a

F=`1200xx0.2N`

F=240 N

Thus, each person pushes the motorcar with a force of 240 newtons.