How much zinc sulfide should the chemical plant have on hand in order to prepare 2.0x10^$kg of zinc oxide?

Zinc oxide can be prepared industrially by treating zinc sulfide with oxygen. The byproduct is sulfur dioxide, SO4. An engineer expects to obtain 78% yield of zinc oxide by this process. How much zinc sulfide should the chemical plant have on hand in order to prepare 2.0x10^4kg of zinc oxide?