Task: Question Answering
Input (English): Problem: if money is invested at r percent interest , compounded annually , the amount of investment will double in approximately 70 / r years . if pat ' s parents invested $ 7000 in a long term bond that pays 8 percent interest , compounded annually , what will be the approximate total amount of investment 18 years later , when pat is ready for college ? 
Options: a ) $ 28000 , b ) $ 15000 , c ) $ 12000 , d ) $ 10000 , e ) $ 9000
Output (English): a