How do you work out 50x4 the whole number multi digit common core way?

The variable z is directly proportional to x, and inversely proportional to y. when x is 4 and y is 13, z has the value 1.2307692307692. what is the value of z when x= 9, and y= 20

Joseph haydn pet store offers wide variety of leashes for dogs. the store purchases one popular type of leash from its manufacturer for $4.38 each. joseph haydn pets marks up leashes at a rate of 238% of cost. what is the retail price of the popular leash?

Roger could feed 5 walruses with 4 kilograms of fish. how many walruses could he feed with 7.2 kilograms of fish?