Hi there. I am so confused on this problem. Would really appreciate some help?

A 3183 H z , 100 dB sound wave is recorded, inverted electronically, and played back with a delay ∆t = 5 × 10E− 6 s. How loud (in decibels) are the two waves combined? What time delay ∆t would be needed to cut the combined intensity by 40 dB compared to the original sound?