Income of the first account after x years:

Income of the second account after x years:

Equating the above tw values we get the equation:

Solving the above equation for x:

Answer 8 years.
combine your like terms and get x by its self
Answer:
the digit two is in tens... so a) is the answer
Well, you can't really determine the price of 1 book, but you can find out the average cost.
280 - 16 = 8x (x = cost of 1 book)
264 = 8x
264/8 = 8x/8
33 = x
So the average cost of one book is 33$( A little expensive if I do say so myself)
Hope this helped!