Given data:
* The mass of person A is,

* The mass of person B is,

Solution:
The diagrammatic representation of the given case is,
The weight of person A is,

The weight of person B is,

The normal force in the upward direction acting on person A due to the ground is equal to the weight of the person.
Thus, the net normal force acting on person A is,

Here, the negative sign indicates the direction of the net force is vertically downward.
Thus, the magnitude of normal force on person A is 490 N.
(B). If person B carries a helium balloon with an upward lift of 300 N, then the weight of person B is decreased to,

Thus, the magnitude of normal force on person A is,

Hence, the normal force on person A, in this case, is 190 N.