The loudness of sound is measured in decibels in honor of Alexander Graham Bell (1847-1922), inventor of the telephone. If the variation in pressure is $P$ pounds per square inch, then the loudness $L$ in decibels is $$L = 20 \log_{10}(121.3 P).$$ Find the variation in pressure caused by a rock band at 115 decibels.

Answer: pounds per square inch.