Task: Question Answering
Input (English): Problem: i sold a book at a profit of 10 % . had i sold it for $ 90 more , 15 % would have been gained . find the cost price ? 
Options: a ) $ 1800 , b ) $ 2500 , c ) $ 3000 , d ) $ 3120 , e ) $ 1540
Output (English): a