There are 15 books on the shelf. All of the books are either about Winston Churchill or Queen Elizabeth. There are twice as many books about Winston Churchill than there are about Queen Elizabeth. How many books are there about Winston Churchill?
+36915 w = # churchill books
e = # QE books = 1/2 w
w + 1/2 w = 15
1.5 w = 15
w = 10 books about churchill
