Task: Question Answering
Input (English): Problem: mary invested a certain sum of money in a bank that paid simple interest . the amount grew to $ 260 at the end of 2 years . she waited for another 4 years and got a final amount of $ 380 . what was the principal amount that she invested at the beginning ? 
Options: a ) $ 200 , b ) $ 220 , c ) $ 230 , d ) $ 240 , e ) $ 250
Output (English): a