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The amount paid for your additional share of the company is not currently deductible. However, it adds to your basis in the LLC, so if you dispose of your share of the company, it will reduce the amount of gain recognized on the disposal. If part of each payment represents interest on the loan, the interest is deductible on schedule A of your personal return as "Investment Interest". But the principal portion of the payment is just a payment on the $30,000 purchase price.
So, the answer to your question is: you will be able to deduct the $30,000 eventually when you sell your interest in the company. In the mean time, make sure you keep track of your basis in the LLC so you will get that deduction.