The weight of an object is the product of its mass, m, and the acceleration of gravity, g (where g=9.8 m/s2). if an object’s mass is m=10. kg, what is its weight?

You just told us that  Weight = (mass) x (gravity),
and that mass=10kg and  gravity = 9.8 m/s².

All we need to do is write those numbers in place of the letters.

                     Weight = (10 kg) x (9.8 m/s²)  =  98 newtons.

Fitness is the ability to perform only very light levels of physical activity.