Task: Question Answering
Input (English): Problem: the temperature of a certain cup of coffee 15 minutes after it was poured was 120 degrees fahrenheit . if the temperature f of the coffee t minutes after it was poured can be determined by the formula f = 120 * 2 ^ ( - at ) + 60 , where f is in degrees fahrenheit and a is a constant . then the temperature of the coffee 30 minutes after it was poured was how many degrees fahrenheit ? 
Options: a ) 65 , b ) 75 , c ) 80 , d ) 85 , e ) 90
Output (English): e