Gain Bandwidth Product for OpAmp

Ask

EC.27)The gain bandwidth product for a 741-opamp , given the closed loop gain,$ A_v=80dB $and the cutoff frequency at that gain $f_c=80Hz$ is 
(a)800k 
(b)80k 
(c)8k
(d)none of the above

Answer is (a)

Concept

Given , $20 log_{10} A_v = 80 dB; \implies A_v = 10^4$.

Bandwidth product is given by $A_v\times f_c $ = 10^4 \times 80 = 800k