Threshold Detection With Gaussian Noise

Two sources of noise, adjacent to each other in a room, have sound pressure levels of 30 and 40 decibel (dB). The combined sound pressure level in the room is _________ dB(rounded off to 2 decimal places).
Use reference sound pressure as .

An industrial stack emits 100 g/s of CO at an effective height of 'H', where the wind speed is 5 m/s. At 3 km distance downwind, the values of dispersion coefficient in y- direction and z-direction are 50 m and 25 m, respectively. The CO concentration at the centerline of the plume at 3 km distance downwind is ________ (rounded off to 2 decimal places)? Use Gaussian plume model and value of = 3.14. Neglect reactions and the ground effect of plume in the calculations.