Let us assume that I initially had a sensitivity of -90 dBm. Now due to some reason the sensitivity got increased to -84 dBm. This means that we have an increase in sensitivity of 6 db. So 6 db increase in sensitivity indicates how much increase in the transmitter power so that the range is same?

I got the answer as 4 times the initial power but the correct answers seems to be 2 times. Which one is correct?

Thanks