Question 455092
Let x = the diagonal of the rectangle with a length of 5 ft and width of 3 ft
    y = the length of longest object that will fit inside the box

  X^2 = 5^2 + 3^2
      = 25 + 9
      = 34
  y^2 = x^2 + 4^2
      = 34 + 16
      = 50
    y = 7.07 (square root of 50)

The length of the longest object that will fit inside a rectangular box is 7.07 ft.