You can put this solution on YOUR website! find the logarithm of each using log2=.30,log3=.48 and log 7=.85
log 21 = log(3*7) = log(3) + log(7)
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log3^5 = 5*log(3)
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log 10.5 = log(3*7/2) = log(3)+log(7)-log(2)
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Cheers,
Stan H.