Task: Question Answering
Input (English): Problem: the perimeter of an equilateral triangle is 60 . if one of the sides of the equilateral triangle is the side of an isosceles triangle of perimeter 45 , then how long is the base of isosceles triangle ? 
Options: a ) 5 units , b ) 10 units , c ) 15 units , d ) 20 units , e ) 25 units
Output (English): a