To calculate the average you must add the percentages up and divide by the number of percentages. So, 52+28+34+95+16+63=288/6=48. The percentage is 48%.
For the second questions you take 100 divide by 3 since there are 3 coins and you get an 33.3%. But, since you can't have 0.3 of a coin. So, since you started with a nickel, you would end with a nickel giving you a percentage of 34% and the dimes and quarters a percentage of 33% each.
The books are $5, and the magazines are $10. I’m not sure which way you want it explained but since magazines are twice the price of books, you can solve the equation 3b + 2b = 25. This gives you b=5 which you just multiply by 2 giving you the price of a magazine.