On a basic P.A system, at a particular amplifier setting, the system will howl if 1% of the output power is fed back to the microphone. Estimate the power gain of the P.A. amplifier in decibels.​

I was using Gf = G/1 + GH and convert to dB using 10 log x.​

No other figures/details given. Can anyone help?​

 

I think you are on the right track....

By using
1+GH=0
to define the onset of instability
where G is the power gain magnitude setting and H=.01 [the 1% condition]

Find G and GdB=10log(|G|)