Task: Question Answering
Input (English): Problem: balls of equal size are arranged in rows to form an equilateral triangle . the top most row consists of one ball , the 2 nd row of two balls and so on . if 19 balls are added , then all the balls can be arranged in the shape of square and each of the sides of the square contain 8 balls less than the each side of the triangle did . how many balls made up the triangle ? 
Options: a ) 465 , b ) 2209 , c ) 2878 , d ) 1210 , e ) 1560
Output (English): a