A deep-space probe retrieves a dust sample from a comet's tail. Mass spectrometry analysis of the silicon content in the silicate minerals reveals the presence of three isotopes:

• 92.21% of the atoms are silicon-28
• 4.70% of the atoms are silicon-29
• 3.09% of the atoms are silicon-30

Calculate the relative atomic mass ($A_r$) of silicon in this cometary sample. Give your answer to 2 decimal places.