What mass in grammes of hydrogen sulphide will be required to precipitate 15g of copper sulphide from a copper(2) tetraoxosulphate (6) solution?

Answer 1

write the equation
how many moles of Cu2S in 15g?
The equation will tell you how many moles of H2S to use; convert that back to grams.

Answer 2

Please note that if you start with CuSO4 you will produce CuS and not Cu2S.
CuSO4 + H2S ==> CuS + H2SO4
Note also that a correct IUPAC name is copper(II) sulfate.