Multiply each value by its time weighting. For instance, if a worker is exposed to 86 dB of noise for 13 hours a week, 26 dB of noise for 23 hours a week, and 0 dB of noise for 4 hours a week, you would obtain 86 x 13, 26 x 23 and 0 x 4 (1118, 598, and 0 dB hours, respectively).
Sum the values that you obtained in Step 1. In this case, you will obtain 1716 dB hours.
Add together the time weights to get the total weight. In this case, the total weight is 13 + 23 + 4 = 40 hours.
Divide the value in Step 2 by the total weights in Step 3, to obtain 1716 / 40 = 42.9 dB.