Help (exponential equations)

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).

Given: ac and db are diameters. m∠3=

What is the missing reason in step 5? linear pair postulategivendefinition of complementary anglescongruent complements theorem