One day a human being will land on mars. mars has a diameter of 6786 km and a massof 6.42 × 1023 kg. if you weighed 834 n on earth, how much would you weigh on mars?

Mars radius = 3,393 km
Mars Mass = 6.42 x 10^23 kg
Earth Radius = 6,371 km
Earth Mass = 5.97237×10^24kg

Gravity is directly proportional to mass and

Gravity is inversely proportional to the square of the distance. 

So, we can come up with this equation:
Force = Mass / radius^2

Force Earth = 5.97237 x 10^24 / 6,371^2
Force = 1.471 x 10^17

Force Mars = 6.42 x 10^23 / 3,393^2
Force = 5.577 x 10^16

Earth's gravity vs Mars' Gravity = 1.471 x 10^17 / 5.577 x 10^16
= 2.64

Earth has 2.64 times the gravitational attraction that Mars has.
So, you would weigh 834 / 2.64 =
316 Newtons on Mars.