$5.$ A person standing a certain distance from an airplane with four equally noisy jet engines is experiencing a sound intensity level of $120$ dB$.$ What sound level would this person experience if the captain shut down all but one engine? Hint: You cannot divide the sound level by $4.$ The intensities of the engines add, so the intensity for all $4$ engines together $=$ I $+$ I $+$ I $+$ I $($where I stand for the intensity of just $1$ engine$).$