Whats the coefficient for 9x-20+x²

Me what is the value of x? showing work would be appreciated - ! : )

The decibel level of sound is 50 db greater on a busy street than in a quiet room where the intensity of sound is watt/m2. the level of sound in the quiet room is db, and the intensity of sound in the busy street is watt/m2. use the formula , where is the sound level in decibels, i is the intensity of sound, and is the smallest sound intensity that can be heard by the human ear (roughly equal to watts/m2).

To determine the number of deer in a forest a forest ranger tags 280 and releases them back