I would do it in Buhh I'm working so add all of them(16,18,20) together 6 times then add another 16 and 18 and you will get your answer.
Pounds is the correct unit of measure
It d over 3 u 2 text me if you need more help hope this helps u a little bit more.
Price of book in 1938 = $ 0.10
Price of book in 2011 = $ 2,161,000
Number of years over 1938-2011 = 2011 - 1938 = 73
Annual increase in the price = 
⇒ Annual increase in the price = 
⇒ Annual increase in the price = (1.260302283 - 1 ) × 100
⇒ Annual increase in the price = 0.260302283 × 100
⇒ Annual increase in the price = 26.0302283 %
⇒ Annual increase in the price = 26%
Hence, the comic book price increased by 26% annually