Balanced rock has a mass of about36,000kg. if the acceleration due to gravity is 9.8 m/s2 what is the force that the rock is exerting on its pedestal

That means the rock has a downward force due to gravity of 
(9.8)(36,000) = 352,800 N downwards on a free body diagram. If the rock is balanced, that means the normal force up is equal to 352,800 N. And due to Newton's about equal and opposite reactions, if the pedestal is pushing up on the rock with 352,800 N of force, then the rock is exerting 352,800 N of force onto the pedestal. 

Adozen is 12, and your needing to calculate the weight of one medium egg, so i would do 21/12=1.75 per egg, and check your answer by doing 1.75 * 12= 21 : ) : ): ): ): ) i hoped i