There is an error in the information provided. The acceleration due to gravity cannot be negative as the force of gravity between two bodies is an attractive force. I assume you meant the acceleration due to gravity is 2.15 m/ s^2.
A body's weight on a planet is the force with which it is attracted towards the surface of the planet. This is given as m*g, where m is the mass of the body and g is the acceleration due to gravity.
The mass of the Jupiter Rover is 300 kg and the acceleration due to gravity on the surface of Jupiter is 2.15 m/s^2
This gives the weight of the Jupiter Rover on the planet as 300*2.15 = 645 N
weight is a type of force which depends on the mass of the object and the value for the acceleration due to gravity on a given planet.
The formula is: F(w) = mg where m is the mass and g is the value for g.
In this case:
m= 300 kg
g = 2.15 m/s/s
Therefore: F(w) = 300 * 2.15 = 645 Newtons.
Just a side note: the actual value of g for Jupiter is 22.88 m/s/s