question: If it takes 3 kangaroos traveling at the same speed a total of 18 hours to travel across a highway, how many hours will it take four turtles, each traveling at half the speed of a kangaroo, to do so?
answer: If it takes 3 kangaroos traveling at the same speed, a total of 18 hours to travel across a highway, one kangaroo takes 18/3= <<18/3=6>>6 hours to cross the highway.
  A turtle traveling at half the speed of a kangaroo will take 2*6 = <<2*6=12>>12 hours to cross the highway.
  Four turtles will take a total of 4*12 = <<4*12=48>>48 hours to travel across the highway.
  #### 48