A noisy machine in a factory produces a decibel rating of 75 dB. How many identical machines could you add to the factory without exceeding the 90 dB limit

Ahot-air balloon takes off from the ground traveling vertically with a constant upward acceleration of magnitude g/4. after time interval δt, a crew member releases a ballast sandbag from the basket attached to the balloon. how many seconds does it take the sandbag to reach the ground? (express your answer in terms of δt)