Answer
See answer below.
Work Step by Step
Number of moles of Cu:
$75.4\ g\times 89.5/100 /63.546\ g/mol=1.062\ mol$
x mol of $Cu_2S$:
$x\times159.15\ g/mol+(1.062-2x)\times 95.61\ g/mol=100\ g\times(100-11.0)/100$
$x=0.391\ mol\ Cu_2S$, $62.22\ g$
$(1.062-2x)=0.280\ mol\ CuS$, $26.77\ g$
Mass percent:
$Cu_2S: 62.22\%$
$CuS: 26.77\%$
