Sergio plans to paint the 4 walls of his room with 1 coat of paint. The walls are rectangular, and, according to his measurements, each wall is 10ft by 15ft. He will not need to paint the single 3-foot-by-5-foot rectangular window in his room and the 3.5 foot-by-7-foot rectangular door. Sergio knows that each gallon of paint covers between 300 and 350 square feet. If only 1-gallon cans of paint are available, what is the minimum number of cans of paint Sergio needs to buy to paint his walls?

The book says the solution is 2 but I can't figure it out??

Also, I need to solve the following:

8^(2x + 1) = 4^(1 - x)

The solution is -1/8...not sure why though...any help would be appreciated on these.