8. Two speakers are in a line but one speaker is a distance d behind the other. You are 4.50 m in front of the nearest speaker. The sound is wavelength = 1.50 m. (a) The speakers are in phase. What is the smallest non-zero d if you hear constructive interference? (b) The speakers are in phase. What is the smallest non-zero d if you hear destructive interference? (c) The front speaker leads the back speaker by 90. What is the smallest non-zero d if you hear constructive interference? (d) The front speaker leads the back speaker by 90. What is the smallest non-zero d if you hear destructive interference?