Answer:-The mass of a rock weighs 10.5 lbs on Jupiter weighs 5 lbs on earth.
Explanation:-
Given:- The mass of an object on Jupiter varies directly with its mass on earth.
Let the mass of a rock weighs 10.5 lbs on Jupiter weighs x lbs on earth.
Then by direct proportion, we have

Thus the mass of a rock weighs 10.5 lbs on Jupiter weighs 5 lbs on earth.