Answer
28.09 amu
Work Step by Step
Atomic mass of Si = $(27.977amu\times\frac{92.23}{100}) + (28.976amu\times\frac{4.68}{100}) + (29.974amu\times\frac{3.09}{100})$ = 25.80 amu+ 1.36 amu+ 0.926 amu = 28.09 amu
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