Answer:
3.9
Explanation:
Let's do this. Sally can paint 1/7 of the room in an hour while Steve can paint 1/9 of the room in an hour. 1/7+1/9 = 16/63. Two of them working together can paint 16/63 of a room in an hour. Now, let's divide 63 by 16.
Use a calculator from here.
63/16 = 3.9375
3.9375 rounded to one decimal place would be 3.9 and not 4, since the next number after 9, which is 3, is not up to 5. If it were 5 to 9, then the answer would be 4.