How do i do this two column proofs?

Two variables, x and y, vary inversely, and x=12 when y=4. what is the value of y when x=3?

Amachine part consists of a half sphere and a cylinder, as shown in the figure. the total volume of the part is π cubic inches.

Afactory buys 10% of its components from suppliers b and the rest from supplier c. it is known that 6% of the components it buys are faulty. of the components brought from suppliers a,9% are faulty and of the components bought from suppliers b, 3% are faulty. find the percentage of components bought from supplier c that are faulty.