Task: Question Answering
Input (English): Problem: factory x ' s bulbs work for over 5000 hours in 78 % of cases , whereas factory y ' s bulbs work for over 5000 hours in 65 % of cases . it is known that factory x supplies 90 % of the total bulbs available . what is the chance that a purchased bulb will work for longer than 5000 hours ? 
Options: a ) 76.4 % , b ) 76.7 % , c ) 77.4 % , d ) 75 % , e ) 73.9 %
Output (English): b