Atomic weights: -

Pb = 207,2

Sb = 121,76

O = 16

Let the mass of Sb be x grams

Then mass of Pb is (1,34 - x ) grams.

In Sb2O4 the ratio of O to Sb is the same as in SbO2

Therefore 121,76 g Sb combines with 32 g O2 and

207,2 grams of Pb combines with 32 grams of O2

So oxygen that reacts with Sb = 32x / 121,76

and O2 that combines with Pb = 32/207,2 X (1,34 - x)

Total combined O2 = 1,558 -1,340 = 0,218 g

Therefore: -

32x/121,76 + (1,34 -x) X 32/207,2 = 0,218

Simplify 32X207,2x + 5221,0688 - 3896,32x = 5499,85

6630,4x + 5221,0688 - 3896,32x = 5499,85

2734,08 x = 278,781

x = 0,10197 grams

Sb = 0,102 g

Pb = 1,238 g

Therefore Sb = 7,61%