What is the theoretical yield of C6H5Br if 42.1g of C6H6 react with 73.0g of Br2?

how do you calculate the theoretical yield?
and
why is the molar mass 0f Br2 73.0g instead of 160g(using the rounded periodic table)?

In a system with only a single force acting upon a body, what is the relationship between the change in kinetic energy and the work done by the force? answers: work is equal to the change in kinetic energy.work depends on the square of the change in potential energy.work is equal to the negative of the change in kinetic energy.work is equal to the square of the change in kinetic energy